In those cases I tend to leave a comment and vote/flag as unclear. That serves double propose:

1. If the question is left as unclear, it gets closed *until* there is enough information to provide a correct answer.
2. If the questioner itself doesn't take care about the question, it will get closed and deleted. We can't take care of something the one asking doesn't.

If you see a question without the critical information that will allow you to write a concise, close it. That way we can identify the questions that can possibly have answers.

Summary: you ask in comments for clarifications, and answer when the question is clear enough to allow you a correct answer.