How do you say in french i not know what are talking about?

Here are a few ways to say "I don't know what you're talking about" in French, with varying levels of formality:

Informal:

* Je ne comprends pas ce que tu racontes. (I don't understand what you're saying.)

* Je ne sais pas de quoi tu parles. (I don't know what you're talking about.)

* Je n'y comprends rien. (I don't understand anything.)

Formal:

* Je ne comprends pas ce dont vous parlez. (I don't understand what you're talking about.)

* Je ne sais pas de quoi vous parlez. (I don't know what you're talking about.)

* Je suis désolé, mais je n'ai pas compris. (I'm sorry, but I didn't understand.)

More emphatic:

* Je n'ai absolument aucune idée de ce dont vous parlez. (I have absolutely no idea what you're talking about.)

* Vous me perdez complètement. (You're completely losing me.)

The best option for you will depend on the context and your relationship with the person you're speaking to.