"Which channel do you like to watch?"
Translation:Який канал ти любиш дивитися?
you don't necessarily need to repeat "ти". it should also be correct: Який канал любиш дивитися
While pronouns are sometimes dropped in dialogues and in other contexts, this usually sounds too colloquial. This course generally doesn’t accept variants that are too colloquial. I don’t think this should be accepted.