have a clue
not have a clue
To know absolutely nothing (in general, or about something specific). My brother thinks he can maintain his social life after he has kids. He doesn't have a clue! You don't have a clue how that thing works, do you?
have a clue (about something)
Fig. to know anything about something; to have even a hint about someone or something. (Usually negative.) I don't have a clue about where to start looking for Jim. Why do you think I have a clue about Tom's disappearance?