As a first draft there's a variety of fairly simple, fixable problems with this movie and a few major core problems which we're going to have to discuss at greater length. You're an experienced writer at this stage, so you know what the editorial red pen is like, so let's just get right into it. We'll cover the simple stuff first.
D-O doesn't do anything, scrap it. It just wastes screen time. That's an easy edit.
Finn says he has something to tell Rey but gets cut off. We never find out what it was. So how about this: edit those lines out completely and forget about it.
Palpatine wants Rey to become a vessel for him in the conclusion of the movie, so the line at the beginning where he tells Kylo Ren to kill her should probably be cut or replaced.
This whole subplot with Hux being a spy, exposed by Pryde, killed and replaced by Pryde is pointless. Axe the spy subplot, axe the Pryde character and give all his lines back to Hux. Figure out another way for our heroes to evade execution at the last instant instead of being rescued by Hux. No, don't have an explosion go off which inexplicably kills everybody in the room except for our heroes. We already did that in The Last Jedi. Oh wait, that also happens in this movie?
There's a scene here where Finn and Poe are running along Star Destroyer corridors blasting stormtroopers left and right, and the stormtroopers just drop dead immediately after a chest shot, right to the heavy part of their armour. No, I love it, great action piece. But at the end of the scene, Poe, wearing no armour at all, is shot in the gut with a near-identical weapon and he's... fine? Fairly easy fix, I won't bore you with the options.
Palpatine's final arena can't simultaneously be buried deep underground, reachable only via intimidatingly scary elevator platform, and exposed to the sky so he can Force lightning the entire battle. You've got to pick one.
It doesn't make sense that Finn and Poe don't kiss at the end.
I agree that if you're going to insist on having C-3PO around then you've got to do something with him. I agree that erasing his memories and having him stumble around amnesiac for a while is pretty funny. You got some pretty entertaining jokes out of it. ...No, the problem you have here is this weird scene right in the middle where you suddenly play it as sombre? Like he's dying? This is clearly wrong. There are no stakes or tension, because we already established his memory backup earlier... and then right afterwards you're going straight back to the comedy, which immediately undermines any sense of grief we had. The easy fix is to play the entire thing for laughs. When he gets his memories back at the end, that becomes an amusing relief rather than the conclusion of a near-death experience.
(So you used that now-deleted "one last look at my friends" scene in the trailer, who cares? There's no law which says anything in the trailer has to be in the movie. Ask the Rogue One people.)
Get rid of the fight with evil Rey. You put that scene there because it was in Empire but it wasn't in The Last Jedi and you wanted to make up for it, but actually it was in The Last Jedi. It's the scene where she's in the haunted hole on Luke's island and she confronts versions of herself. Go watch it again. See?
You have an obsession with absolutely absurd ticking clocks. Mission: Impossible III had the same problem (and honestly so did The Last Jedi). If I'm reading this right, almost all the events of this movie are supposed to take just sixteen hours of in-universe time? No. Just, no. The movie moves at a crazy enough pace that you don't need this. There's enough urgency in how it's edited already, trust in that!
(I'm sorry, the final scene on Tatooine is later the same day? Are you joking? Oh, you are joking.)
If Rey's healing power comes at the expense of some of her own life energy, she should be visibly hurt or sick after helping that slug creature, and again later after healing Kylo Ren's stab wound. Otherwise Ben should just be able to resurrect her for free at the end, right?
The flashback with Luke and Leia fighting is pointless gratuitous fan service and gives us nothing, cut it. I know you want to see Leia wielding her lightsaber in her prime. Too bad, mate.
You can have Poe describe the Holdo manoeuvre as a one-in-a-million absolutely unrepeatable freak occurrence or you can show the aftermath of a Holdo manoeuvre in the sky over Endor in the closing montage, establishing it as a now-standard technique, but not both. I'd suggest the first one since it's the one which doesn't completely break the Star Wars universe.
Re Ochi's ship: you seem to think that sitting exposed to desert winds for two decades doesn't have any meaningful effect on a spaceship's spaceworthiness. Do you have any clue what that amount of sandblasting does to a delicate machine? It would still be there, sure, but it should be a non-functional wreck. ...Old technology, huh? "Used future"? Spaceships in Star Wars are like cars in reality? Alright, I'll buy that. But then let me ask you this: Why did nobody steal it? Or siphon off its fuel? You know spaceships have fuel, right? This was a pretty big plot point in The Last Jedi. You did watch The Last Jedi, I assume.
Or at least, how come nobody stole any vital parts from the thing? There are plenty of scavengers in this Galaxy, people who raid wrecked ships for valuable parts and sell them, just to survive. Jannah, for example. The fact that she's a scavenger is mildly important to the plot. Or Rey! You had this problem in The Force Awakens too. Next time around, I suggest not having Rey be a scavenger of decades-old Imperial wrecks while the Falcon is sat right there in her neighbourhood junkyard in perfect working order. It's just this glaring contradiction.
While I'm at it, based on this and Star Trek Into Darkness, I feel like you have absolutely no conception of what happens to a spaceship when it gets immersed in water either. Especially for long periods of time. Does even an Earth car work after sitting in a lake for the same amount of time that Luke's X-Wing was underwater?
Oh, forget it. You can have this one. It's not like I noticed this exact same problem in Empire when I was a kid.
The closing scenes of the final film of a trilogy of trilogies are probably not the best time for raising questions like "Is Jannah Lando's daughter?" Even if they were, while you have an amazing talent for creating truly riveting mysteries — I cannot deny the audience figures, Lost hooked even me at first — "Is Jannah Lando's daughter?" is an incredibly poor excuse for a mystery. This is not an open-ended question, it's a binary yes/no. But more importantly, nobody cares about either of those possible answers. They're related! Who cares? They're not related! Who cares? No, I'm not saying scrap that scene. I'm saying scrap the character of Jannah entirely.
Kill Chewbacca. Don't reveal it as a stupid fake-out sixty seconds later. Have some creative grit. Follow through. I know test audiences hated it. That's because it raises the stakes. It's fine, the bit with the medal becomes bittersweet.
Well, since we're here, let's scrap the medal thing completely. Because? Let me spell it out for you: if Chewie wanted a medal, they'd have damn well given him one. The guy tears arms off! Just try telling him "no"!
Heck, he served with Yoda in the Clone Wars; probably he already has a medal. And none of that has changed, so why would he want or need one now when he didn't before? I think you think you're resolving a long-unanswered question here but actually you're just raising more confusing questions. Just scrap it.
How in the Galaxy does Rey know how to sail? She's from a desert planet, if anything the ocean should be the most terrifying thing she's ever— oh, never mind. Let's move on.
Okay, let's get into the harder stuff.
How did Palpatine survive Jedi?
No, I know it's not stated clearly in the cut of The Rise of Skywalker we just saw. I know it's intentional ambiguity. I got that. I'm asking you, as a fellow writer, to tell me in plain language how Palpatine survived the events of Return of the Jedi.
You don't know. Okay, so, that's terrible writing. Firstly, it's unconscionably lazy; you owe the audience more than that. Even if you don't plan to share your answer, you should do the leg work. Secondly, if the audience doesn't know how Palpatine survived, what's the first explanation they're going to think of? Cloning. And if cloning is how Palpatine survived being thrown in a shaft and exploded in Return of the Jedi, why would anybody think he's genuinely, permanently dead after being atomised on screen in this movie? He'll have spares! Billions of spares. This ruins all finality or catharsis in your triumphant final kill. "I have died many times"? Are you intentionally trying to break the movie? It doesn't work anymore.
Yeah, I love Ian McDiarmid too. He's great.
Anyway, you need to make it abundantly clear that cloning is not the answer to this question. The way to do this is to not mention it or even hint at it at any point in the movie. This scene here, where Palpatine claims to have "made Snoke" while Kylo Ren is walking past a vat containing multiple partial Snoke clones? That's the whole problem. Get rid of it.
"Powerful Sith magic", go with that. Consider a flashback showing how he escaped the Battle of Endor.
Who made the knife? When? Why?
You can't answer that question either. I can help you out. Not with an answer to the question, I'm going to help you remove the question entirely. So, the first half of this movie is an exhausting fetch quest. They run to a planet to get a thing to get to another planet to get another thing to get to another planet. But let's suppose that you were Rey, Finn and Poe, and you were searching for a legendarily rare Sith wayfinder. What is literally, not figuratively, the first place you would look?
The Emperor's throne room in the wreckage of the second Death Star.
So how about this: start with Rey there, on the ocean cliff, on Endor.
Yes! Let it all die! The knife, Pasaana, Kijimi, Lando, Zorii Bliss, the C-3PO stuff. It's okay. It's going to be okay! I know there's a bunch of logistical juggling which falls out of this. You'll need to combine two of Kylo Ren and Rey's lightsaber duels. Keep the Force item swapping, that's great. It's a brand new Force power but at the same time it makes a perfect kind of fairy tale sense. But trust me, the movie is 45 minutes leaner now. You have time to breathe, to explore.
What do you mean the Death Star wreckage isn't on Endor? It was in low orbit around Endor when it blew up, where else would the wreckage land? Where the hell is Kef Bir?
Do you know how space works?
Nearly done, don't worry.
So, as a quick exercise, let's compare the climactic space battle of The Rise of Skywalker with the climax of A New Hope. What would you say is the fundamental difference between these two sequences?
(While we're here, we could also quickly compare the climax of Star Trek: Nemesis with the climax of your far more successful and effective remake of it, Star Trek (2009). They have exactly the same interesting point of contrast.)
So, in A New Hope the Death Star superlaser is pointed at the Rebellion base and about to fire, obliterating it. In The Rise of Skywalker the Star Destroyers' superlasers are pointed at nothing. The threat is totally abstract. It's in the nebulous future. Something bad might happen later if they're allowed to escape. And so, there is no immediate tension.
I know that Poe's zipping around up there, rapidly running out of options, but the trouble with space combat in Star Wars is that it's a totally binary universe where either you're alive or you're dead and there's no halfway. There are no cliff-edge stones crumbling away beneath your grip, there is no bandsaw getting closer and closer while you struggle with the ropes. We don't get a sense that Poe, or anybody else, is getting closer to death. I know you tried to make that the point of tension, but you didn't succeed.
There's no easy fix for this one. I'm just saying, the lasers need to be aimed at something. Or someone. I'll leave it to you. (Pretty soon I'll be writing an entirely new movie of my own.)
Last one. I can't believe I have to explain this one to an experienced Hollywood writer. In the climax, Palpatine presents Rey with an impossible, unwinnable dilemma: let him live and conquer the Galaxy, or kill him, becoming him, becoming the Empress and conquering the Galaxy herself. This is great. It's textbook. Normally, what happens at this point is that the hero takes option three. They use something which they gained over the course of the story — a lesson, a power, a friend — to escape the binary trap and choose victory instead. What happens in your movie, however, is that for no particular reason Palpatine voluntarily rescinds his ultimatum, so that there's no dilemma, and then Rey just does the obvious thing and kills him. She doesn't become a Sith vessel or anything. It's fine.
Just off the top of my head: Palpatine is in awful condition. Maybe Rey could use that healing power which you set up earlier? Maybe Rey can heal the Sith? At some personal cost? But honestly, I would accept anything which isn't "Rey solves the problem by adding lightsabers".
Okay so that's quite a bit to work with. I'll just boil the rest of these down to bullet points. These aren't questions I specifically want you to answer, just have a bit of a think about why these questions impede viewers' enjoyment of the movie:
Anyway, good luck! This is a decent first draft of a movie right now, but I really think with some work it can be made heaps better.