The programs knotes and kjots are now under akonadi control. I looked into it, and notes made with
kjots are either in a MySQL database or, if it's a big note, in a file pointed to from the database.
The akonadi tray icon (akonaditray) offers a backup possibility, which is especially useless if you cannot log in graphically because then you have no systray.
I'm pretty confident, that if you backup .kde and .local, (dot kde and dot local) in your homedir, that you have your files, but do not blame me if I'm wrong..
A complete dump of /home is the best solution!