Since you now type it with a capital N, do you mean the app itself, or the data? Assuming the latter:
I don't use the Notes app, but there's a database in Library/Group Containers/group.com.apple.notes called "NoteStore.sqlite". That may be the database of all notes.
If you are trying to reinstall the stock Notes app, boot your Mac via Command +R. When the Utilities screen appears, click on reinstall OS. Doing so should fix your problem while preserving your personal files.