The trick of turning on highlight moves in the options, then clicking on your king works well if you want to know whether or not YOU can castle, but there's no way of determining whether or not THEY can castle.
How to know if castling is allowed in puzzles?
Sort:
I think that because most of the puzzles in chess.com are not composed by humans, but automatically generated with the help of a computer algorithm (as far as I know), the only fair solution would be to show the castling rights for both sides. Human compositions and studies are a different thing, where there are unambiguous rules.