Critique my Stack Overflow schema
Your answers table doesn't actually have an answerID, which is later referenced in your answer comments.

Your link tables for comments, I would have a primary key assigned that is separate from the answerid, since you don't want a composite key between answerID and comment (Think about updating/removing post logic). Apply the same to question comments.

Consider storing users against questions/answer submissions, otherwise, how will you know who posted it? Think about edit functionality too, do you want to audit changes?