I don't know what you're saying.
I don't know what you are saying.
I don't get what you are saying.
I don't know what you're saying.
I don't know what you are saying.
I didn't know that you didn't know.
I don't know what you're talking about.
I don't know what you're saying.
I don't know what it is you want to say.
I don't know what you mean.
君の言うことなすこと、私にはさっぱりわからない。
I have no idea what you're saying.
I don't know you.
I don't know what you want to say.