what are you talking about?what did you say?

如果是剛才對方說的話我沒聽清楚，所以我再問了一次，可以用：
What did you say?
或
Could you say it again? (用語比較委婉)
Can you say it again?

也可以用在驚訝的語氣
Mirror,mirror, tell me who is the most beautiful women.
You are the most beautiful women. But snow white is the most beautiful women of all.
What did you say?

最好不要用What are you talking about?
因為what are you talking about?用在某種加強語氣，有不耐煩聽別人講的話，對對方說的話表示厭惡或反感，有否定對方言論的味道。
例如，對方在有第三個人的時候說了我的短處，我表示否定，就可以說：What are you talking about?

但是what are you talking about? 最適合表達的是，某群人正在談論一些事情，而你也覺得有興趣，這時湊過去就可以問：
what are you talking about?
你們在討論什麼？