Two rules apply, and the timing has to be prior to the start of the service motion.
4.B.8. Prior to the start of the service motion, to determine the correct server and correct service court, theserving teammay ask the referee the score and “Am I the correct server?” Players may not ask if they are in the correct position.
4.B.9. Prior to the start of the service motion, to determine the correct receiver and his or her position, thereceiving teammay ask the referee to confirm the score. Players may not ask if they are in the correct position.