You have to do your homework in order to TRY to ascertain which groups are on your cruise.
You can do a search on the way for various groups.
You can look http://unofficialcarnivalwiki.com/wiki/Group_Cruises
to see if there are any significant groups booked on the same cruise.
You can visit the various cruise forum boards and look into the different groups and theme boards to see if any groups you are interested in have cruises scheduled for the ship/week you are looking at.
It is time consuming and not always helpful.
(cruzin' solo by design)
Freedom ('09), Imagination ('08), Victory ('08), Destiny ('08), RCCL Navigator ('08), RCCL Majesty ('08), Glory ('07), Liberty ('07), Fantasy ('07), Destiny ('06), NCL PofAm ('05), Fascination ('04), Victory ('04), Fascination ('04), RCCL Voyager ('03), Fantasy ('99)