Currently, only IMAP-based address books allow their respective CardDAV URL to be shown in the web app by using the $config['kolab_addressbook_carddav_url'] variable. LDAP-based address books have this function greyed out and currently do not support it.
The URL for them is constructed with:
Currently, it is not documented how to access the GAL via CardDAV. Using this already existing Show URL feature, would be good way to do it.
However, for various reasons, we can not fully support this feature, so the configuration option should include a big fat comment to that extent and tell users to only enable this feature if they are ready to deal with the fall-out.