is
NotificationSound as a text which can play when notification come (sound will be text to speech)
is
NotificationSound as a text which can play when notification come (sound will be text to speech)
I do not know what "NotificationSound" is. But to have a notification play a sound you need to set:
CKNotificationInfo *notification = [CKNotificationInfo new];
notification.soundName= @"welcome.wav";
where "welcome.wav" is a sound file in your "Copy Bundle Resources" list under "Build Phases" for the target.