Notes have vanished from iPad
Open notes shows no notes iCloud on signed in
iPad, iOS 10
Question marked as
If you are syncing your notes with iCloud, can you see your notes, if you log into your iCloud account on the web browser of your computer?
If you can't, did you check the Recently Deleted folder?
Have a look at the troubleshooting mentioned in this related article:
If you're missing notes on your iPhone, iPad, or iPod touch - Apple Support