Checking on your Pokemon’s status with you is important in Pokemon Brilliant Diamond and Shining Pearl, especially if you want to evolve certain types of creatures in the world. Thankfully, you can do so with the Friendship Checker that can be found relatively early in the game.
As soon as you reach Eterna City, you’ll find all manner of shops and services available to you. However, to find the Friendship Checker Poketch app, you’ll need to go into the city’s Pokémon Center. In the main lobby, you’ll find a nice lady with long brown hair, a pink shirt, and a green skirt. She’s standing on the Pokéball emblem on the main floor. Go talk to her and she’ll give you the Friendship Checker Pokétch app. It’s easy to find her, and thankfully, she won’t request you to go on some errand in exchange for such generosity.
To use the Friendship Checker app, press the right shoulder button. Now, hover the mouse-like hand to the red button on the side of the game’s device. Keep pressing it until you see a screen with your party’s Pokemon walking around. Press A to see how they feel. If they are jumping up, they’re happy with you. There’s much more to friendship levels in Brilliant Diamond and Shining Pearl to understand, but this app gives you some basic feedback on how each of your party members is feeling about you.
While you’re around Eterna City, you can go find a Ponyta. They are running around in green patches of grass in this area of Sinnoh.