Why is "Słuchasz muzyki." not accepted? Is there a rule when you have to add the personal pronoun ("ty" in this case)?
It should have worked. Subject pronouns are most commonly omitted.
Słuchać requires Genitive
Słuchać zenona martyniuka
I guess if you say "do muzyki" it's incorrect?
Yes, it's incorrect.
Why "Czy sluchacie muzyki" doesn't count?
Czy is an interrogative particle, but this sentence is not a question.
Why is "Ty sluchasz muzyki" not correct? and "Wy sluchacie muzyki" is correct? How am I to know if it is "you" singular or "you" plural from this sentence?
"Ty sluchasz muzyki" is displayed on top of this very page, so it's definitely accepted.
Ty... was my answer and it was not accepted. ????
I don't see any recent reports, so the most likely explanation is that you made an error somewhere.
Why not pan słucha muzyki?
Formal You forms are still missing here and there. Added here.