have a clue
• know about something or about how to do something.
• "I didn't have a clue what was happening"
Similar:
have no idea,
not have any idea,
be ignorant,
not have an inkling,
be puzzled,
be perplexed,
be bewildered,
be baffled,
be mystified,
be at a loss,
be (all) at sea,
be clueless,
not have the faintest,
