Right answer:
escuchan
This is a question that stands for the second person singular, which is ustedes. This subject pronoun is more common in Spanish speaking countries either in formal or informal conversations. In Spain, it's more common to use vosotros in informal conversations. On the other hand, escuchan is the conjugation of the verb escuchar that matches this person. Finally:
¿Qué escuchan Uds.?
A response to this answer could be:
Nosotros escuchamos Rock
