WoW:API GetComboPoints

GetComboPoints()

Delivers how much combo points the rogue or the druids cat form on the actual target has.

 local comboPoints = GetComboPoints();

 if ( comboPoints == 5 ) then

   print "You have 5 Combopoints, use a Finishing Move!";

 end

The return value is a number (0 up to 5).