In those cases I tend to leave a comment and vote/flag as unclear. That serves double propose:
- If the question is left as unclear, it gets closed until there is enough information to provide a correct answer.
- 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.