「聞く」 (kiku) is a versatile verb meaning "to listen," "to hear," or "to ask." When listening/hearing, it takes を (o) for the sound source. When asking, it takes に (ni) for the person asked and を (o) for the question. For example, 「音楽を聞きます。」(Ongaku o kikimasu.) means "I listen to music." Or 「先生に聞きます。」(Sensei ni kikimasu.) means "I ask the teacher."

聞(き)くは耳(みみ)で聞(き)く、質問(しつもん)する意味(いみ)。音楽(おんがく)を聞(き)きます。先生(せんせい)に聞(き)きます。