not have the foggiest idea
To have no knowledge or understanding about something. He does not have the foggiest idea how hard it is to run a business. I do not have the foggiest idea where I left my car keys.
not have the foggiest idea
or not have the foggiest
INFORMALCOMMON If you do not have the foggiest idea or do not have the foggiest, you do not know anything at all about something. I did not have the foggiest idea what he meant. `How often does it need to be changed?' — `Haven't the foggiest.'