You'd need to query the database for such information using the CB Query Field. The below usage should work.
Query:
Code:
SELECT GROUP_CONCAT( b.`title` SEPARATOR ', ' )
FROM `#__user_usergroup_map` AS a
LEFT JOIN `#__usergroups` AS b
ON b.`id` = a.`group_id`
WHERE a.`user_id` = '[user_id]'
GROUP BY a.`user_id`
Output: Single Row
Columns: Single Column
That should give you a comma separated list of usergroup titles.
krileon
