number of the unit group

is there a way to know the number(s) of the group for an unit ( Ctrl+X) ?

i dont think there is, since that is local. and jass is not local. so dont think u can retrieve that number into a variable or anything

maybe with a custom native ?

constant native IsUnitInGroup takes unit whichUnit, group whichGroup returns boolean
maybe work with that native.

unless you create a grouping system in your map and check every single group you created/used in the map with the unit and return them to an integer... I cant think of any other way...