I did not have the foggiest idea what he meant.

我压根儿不知道他是什么意思。

I haven 't the foggiest idea what it is.

那是什么我根本就不知道。

I don't have the foggiest idea how to do it.

我对于到底要怎么做一点概念都没有。

I haven't the foggiest idea what you are talking about.

我一点也听不懂你们在谈些什么。

I don't have the foggiest idea about what I think about international foreign policy.

关于国际外交政策，我甚至没有最模糊的想法。