Most doctors don't have the foggiest idea about migraines.大多数医生根本不清楚偏头痛是怎么回事。

not to have the foggiest idea what …对…一无所知

I did not have the foggiest idea what he meant.我根本不知道他是什么意思。

not to have the foggiest notion what …对…根本没什么概念

I haven't the foggiest notion what she might like.我对她可能喜欢什么一点儿概念也没有。