How long does it take to get to Okinawa by airplane?
Literal
Airplane [by-で] Okinawa [to-に] go [purpose-のに] how-much time [subject-が] takes [question-の]?
~のに marks purpose: 'for going to Okinawa.' The sentence-final の is a casual question marker. 沖縄 (おきなわ) is Japan's southernmost prefecture — a popular domestic travel destination.