have a clue

not have a clue

1. To not have even a remote grasp or understanding of something; to be hopelessly confused or ignorant about something. You'd expect the average citizen to struggle to explain the workings of government, but now it seems like even most politicians don't have a clue! You don't have a clue about how to talk to people, do you? When it comes to trigonometry, I just don't have a clue.
2. To be completely unaware of something. A: "Do you think Paul suspects that we're having a surprise party for him? B: "No, he doesn't have a clue!"
See also: clue, have, not
Farlex Dictionary of Idioms.

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?
See also: clue, have
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.
See also:
  • (I) wouldn't (do something) if I were you
  • a/the feel of (something)
  • a straw will show which way the wind blows
  • a crack at (someone or something)
  • all right
  • (you) wanna make something of it?
  • a fast talker
  • all for the best
  • a thing of the past
  • a slew of (something)
References in classic literature
As long as this man has no idea that anyone can have a clue there is some chance of securing him; but if he had the slightest suspicion, he would change his name, and vanish in an instant among the four million inhabitants of this great city.
A Study In Scarlet
Del Monte Foods, who conducted the survey, said most Americans admit they are not getting the daily recommendation of fruits and vegetables and "don't have a clue when it comes to understanding the new Dietary Guidelines for Americans".
Survey finds Americans do not enough fruit and vegetables
"I did not have a clue what I wanted to do as a career, so I joined Three A's Pertemps Training.
Fatherhood was the inspiration for Matt; Jobs & New Directions