You may be able to find the notes in your iPhones ‘Recently Deleted’ folder, but if the notes are no longer there, you can use Recovery data recovery software to help you locate and recover the notes you are missing.
It’s also possible that you can recover your lost notes through your iTunes or iCloud backup files, although overwriting your iPhone with these files brings its own data loss risks. MobiKin Doctor for iOS can help to minimise these risks and recover only the specific data you have deleted.