Listen, there are some things we cannot answer. You’re telling us that your notes vanished while connecting your iPad Pro to a Logitech keyboard. I can’t find a correlation between the connection and the disappearance of your notes. Since you stated that the notes are not associated with iCloud, I’m going to assume they are saved locally on the device.
With that being said, start by rebooting your iPad Pro. Afterwards, initiate the native Notes app and then tap on the arrow in the upper left corner of the screen until you see “FOLDERS”. That should provide you with a count of all of your notes in their associated folders. Select them all to see if your notes have reappeared.