Welcome back,
@Tisztul_A_Visztula !
Actually, the original sentence is not correct. It should be
Večer pozerám televízny program, without
sa. The corresponding question would be "Čo pozeráš večer?", the expected answer being the name of a TV show or a TV channel.
I find the whole family of
pozerať/pozerať sa/pozerať si hard to explain, and even the dictionary definitons
Slovenské slovníky didn't help me much.
I think I use
pozerať + direct object essentially in
pozerať televízor, pozerať (niečo v televízii - film, futbal).
For a
film v kine, I would prefer
pozrieť si + direct object, althought I couldn't tell why.
In other situations of watching/looking, either
pozerať or
pozerať sa can be used, but usually with
na niekoho/na niečo.
In fact, a direct object is not possible with
pozerať sa. (As a rule, "sa" verbs do not take direct objects; the only exeception I can think of is "učiť sa".)
Anyway, back to your question:
A) "Čo pozeráš večer?" is an idiomatic way to ask "What do you watch in the evenings?" or even "What are you watching tonight?" and the presupposition is that the person watches TV or Netflix or something similar.
B) "Na čo (sa) pozeráš večer?" is grammatically well-formed but feels odd, a bit like "What do you look at in the evenings?". It presupposes you look at something, but the possible set of answers is too wide (The walls? The sunset? The moon? The neighbors fighting?).