1. What dorm doesn't have air conditioning. (Replace /don't/ with /doesn't/)
2. Where is your paper? (Omit the "at")
3. Oh, I ate too much! (Replace /two/, which means 2, with /too/, which means "excessively.")
4. Jane doesn't work here anymore. (Replace /hear/, which refers to the action of hearing with your ears, with /here/, which means "in this place")
5. ( I see nothing wrong with this one...)
6. No thanks, I don't want any of that cake. (Replace /none/ with /any/; none is incorrect because with /don't/ it forms a double negative)
7. The man who stole the car was caught. (Replace /which/ with /who/; you're referring to a person, not an object)
8. This antique vase is unique. (Omit /very/; if something is "unique" it's the only one like its kind, making adverbs like "very" unnecessary)
9. Needless to say, we won every game. (Combine the independent clause and the dependent clause using a comma)
10. I don't know that you can figure this out. (Omit /but/, as its presence just confuses the meaning of the sentence; it has no place here)
11. It's too late; I've already burned the dinner! (Add an apostrophe to /Its/; its without an apostrophe indicates possession. Here the meaning is a contracted form of "it is," so it needs an apostrophe)
12. (I see nothing wrong with this one either... Maybe it calls for "Charlie's Angels" to be put in italics, but I can't be certain)
13. ABC leads in the network ratings because it has better shows. (Remove all the "due to the fact that phrases as they are redundant and unnecessary)
14. (Nothing wrong with this one, that I can tell.)
15. (I think this one is fine as well.)
16. Jack will pay if he flaunt the law. (Just invert the sentence to make it shorter and more to-the-point; /flaunt/ doesn't really make sense in this sentence, but I'm not sure if you're supposed to introduce new words)
17. Pat Hayden threw the ball farther than the opposing quarterback (Replace /further/ with /farther/, as the latter refers to physical distance, while /further/ is used in the place of /additionally/ in writing)
18. (Looks completely fine to me)
19. Will you loan me a few dollars until/till Friday? (/'til/ is outdated and not used anymore, instead, use /until/ or /till/)
20. There were less people than I expected at the party this week. (Invert the last two parts of the sentence so that it makes more sense grammatically)