not have the foggiest (notion)
To have no knowledge or understanding about something. He doesn't have the foggiest notion how hard it is to run a business. A: "Do you know where the car keys are?" B: "I haven't the foggiest. Sorry."
not have the foggiest (idea or notion)
have no idea at all. informal, chiefly Britishnot have the ˈfaintest/ˈfoggiest (idea)
(British English, informal) have no idea at all about something; not know anything at all: I haven’t got the faintest idea what to buy Roger for his birthday.‘Where are we?’ ‘I’m afraid I haven’t the foggiest.’