in golderod city is a frienship rater
Chat with our AI personalities
You can get the friendship checker in HeartGold at Goldenrod City. Talk to the happiness rater and she will say a phrase that indicates your Pokémon's happiness. This determines your friendship levels.
In Pokemon Diamond the Friendship Checker (also called the Happiness Checker) app is #6.
Get some mates.
Fly/walk to Eterna City and go into the Pokemon center. Talk to the girl inside there and she will give you the friendship checker.
in goldenrod on the right side of the town