Sound doesn’t worm in iPad
sometimes the sound doesn’t on my iPad. when i turn the iPad off and on again it works again
Is this sound from audio/video apps, or notification sounds? If notification sounds are not audible, be sure that "Do Not Disturb" is not enabled (see the "moon" icon in Control Center). If audio/video sounds are muted, is it all apps or just certain ones? You might try force-quitting the offending app if it is limited to only certain ones.
If none of that helps, as a last resort you can backup your iPad (to iTunes or iCloud) and restore it. That may repair some underlying glitch, but sometimes your backup can be corrupted and perpetuate the problem even after restoring (in which case you'd restore w/o a backup, but that means re-doing everything).