In the 4th gen (DPPT) you can use your Poketch and find out. It should be #06(the one after your party) and if you don't have it you can obtain it by speaking to the lady in the Pokemon Center in Eterna City.
For a visual aid see this website: http://www.serebii.net/diamondpearl/poketch.shtml
well you need to have the poketch apps (the happiness checker) you can get this at the pokemon center in eterna city,talk to the woman in there
