The default address book database is stored at ~/.kde/share/apps/kab/addressbook.kab, any new databases that you have created will be stored wherever you put them.
The file ~/.kde/share/apps/kab/kab.config holds your Kab "preferences" and the command strings for mail and talk.
~/.kde/share/config/kabrc holds general Kab appearance parameters and a list of the most recently visited address books.
Don't modify these files unless you really know what you are doing (and have made a back up).