2PHRASE 一点儿也不知道;根本没什么概念 If you say that you haven't the foggiest or you haven't the foggiest idea, you are emphasizing that you do not know something. 一点儿也不知道;根本没什么概念 [informal, emphasis]
I did not have the foggiest idea what he meant.
我根本不知道他是什么意思。
'How often does it need to be changed?' — 'Haven't the foggiest.'