Verified answer

Very polite:

何を仰っているのでしょうか?

nani wo osshatte iru node shou ka?

Friendly:

何の話?

nan no hanashi?

hmm, im gonna assume the context youre using 'what are you talking about?' is when someone says something and youre shocked, etc, because that phrase can be used in alot of situations.

it is: 'eh, nani?', which is like 'huh, what?'

or 'nan no hanashi?' which is literally 'of what talk is this?'

何述べているか。

is this like this? Romanji?