I don't know what you're on about.
我不懂你在談什麼。
Well, what do you know? Look who's here!
唷，真想不到！你看誰來啦！
She of all people should know the answer to that.
在所有的`人中，唯有她最應知道那個問題的答案。
I don't know how you can say things like that.
真想不到你怎麼會說出這種話來。
She didn't know what life in a foreign country would be like.
她不知道外國的生活會是什麼樣。