我完全不知道你在说什么。

I ___haven't ___the ___faintest ___idea what you're talking about.

我们在城里迷路了，完全不知道如何返回酒店。

We got lost in the city and ___didn't ___have ___the ___faintest ___idea how to get back to the hotel.

他盯着坏掉的发动机，完全不知道如何修理。

He stared at the broken engine, ___not ___having ___the ___faintest ___idea how to fix it.