Answer:
¿Usted devolverá las gafas de sol?
Step-by-step explanation:
"¿Devolverás las gafas de sol?" work if you are directly asking to one person to return the sunglases. Still a bit informal
"¿Usted devolverá las gafas de sol?" is a little more formal, but still works, not commonly use but is the literally translation of "will you return the sunglasses?"
"¿Puedes devolver las gafas de sol?" is the common one, the literally translation is "can you return the sunglases?"