"이 노래는 내일 들을 거예요."

Translation: I will listen to this song tomorrow.

[ErinJohnso622169]

Shouldn't 'hear' be accepted as well?

[wintertriangles]

That sounds like you won't listen to it on purpose, which 듣다 means. 들리다 is the verb you'd use for your word.

[saye1095]

What indicates that it's "I," not someone else that'll listen to the song?

[Staszek456]

nothing. This really can be anyone. However Duo treats me as a default option in sentences without a proper subject/object. So when you see a sentence without them, just assume that this sentence is in first person