you're telling me

hard telling, not knowing

I don't know.

I'm not telling you

Used to express that someone doesn't need to know something, typically because it is a secret (sometimes used as a way to attempt to hide someone's wrongdoing); may also be used when someone tries to ask for answers while doing an assignment or examination, or private or confidential information, including passwords.

now you're cooking

Used to praise someone for adopting a more effective or suitable method or approach, or to signal that progress is being made.

now you're talking

A phrase indicating agreement with a previously stated suggestion to change a course of action.

there is no telling

Used to indicate that something cannot be known or predicted with certainty.

who are you telling

Used in response to an assertion that one is already fully aware of.