If you: don't sync notes but store them on your device ; and want to backup your notes to restore later on a fresh install of Ubuntu Touch (where you chose to wipe all):
In 16.04, notes are stored here:.local/share/com.ubuntu.reminders/@local In 20.04, notes are stored here:
.local/share/notes.ubports/@local
You can use File Manager app to create a backup without need for terminal:
Open the app and next to Restricted Access click Unlock and enter password; Go to the location above; Copy the @local folder by sliding it to the left and then click the copy icon; Paste it somewhere in your Documents folder (from the menu, top corner) Attach your phone to your PC and copy the backup folder to your PC.Once you've got the got a fresh install with Notes app:
Follow the above steps in reverse and replace the newly created @local folder with your backup folder.
(I know the OP asked this question long ago, but this answer might still help someone with same issue).