Which sentence contains a misplaced modifier? the dog catcher said he would return our dog on saturday. my uncle served steaks on paper plates to his coworkers. the waiter served a burnt piece of toast to the man. my aunt is coming home for the holidays who lives in new york.

Let us first define the meaning of misplaced modifier; it is a word, clause, or phrase that is improperly placed in a sentence which make it refer or modify an unintended word. 
The first, second, and third sentences that are given above sound correct because their modifiers are placed just right.  Only the fourth sentence sounded awkwardly and confusing, because the clause "who lives in New York" is improperly separated from the subject "My aunt", which must be described in the first place, and not the "holidays". 

The sentence will sound and can be understood better if it is written this way,

"My aunt, who lives in New York, is coming home for the holidays."

Statement 2

Explanation:

There are some simple rules to follow when using punctuation.

Rule 1: Use a comma between two long independent clauses when conjunctions such as and, or, but, for, nor connect them.

Rule 2: If the clauses are both short, you may omit the comma.

Rule 3: If you have only one clause (one subject and verb pair), you won’t usually need a comma in front of the conjunction.

Now, lets see what statements in your question need commas.

Does statement 1 need a comma? ❌

It doesn't need a comma, because of rule 3.

Does statement 2 need a comma? ✔

It needs a comma, because giant and impersonal both modify corporation.

Does statement 3 need a comma? ❌

It doesn't need a comma, because hot and new both modify movie, common sense says a comma is awkward in this situation.

Does statement 4 need a comma? ❌

It flows well, without the need for a comma.

I'm always happy to help :)