When listing poem titles, do the commas go inside or outside the quotation marks?
Everything what goes inside quotation marks is a part of quotation (or here title). Commas are not parts of the titles. They are only used as a list separator. So they should be outside quotation marks.
John has read 4 books by Shakespeare: "Hamlet", "Othello", "Romeo and Juliet" and "Macbeth".