You'd say, "what are you watching?" You can use "what are you seeing?" if someone tells you they are going to the cinema later. If you ask "what are you seeing?" when someone is watching TV, it means you think that person is seeing something different from you, even though you are looking at the same thing on TV. Perhaps that person is hallucinating?

With regard to a program on TV; you would normally ask a person; "What are you watching?"

i think "what are you watching?" is okay.