Harthome city in pokecenter the closest person by the door
Eterna City's Pokemon center. Some random dude gives it to you.
proffessor rowan will give you a app to find : zapdos articuno moltres
In jubilife city.
on the touch screen after you receive the app.
you come with it!
It makes the Pokemon you tap 'cry'.
you have to find out how to Hoe if u ask this question again ill post it again
you get it from a person in Solacean town.
get the Poke tech App Poke happyness
The Pokemon Diamond and Pearl series can be watched on the official Pokemon TV website or by watching them using the Pokemon TV app for iOS and Android. You can also download the Diamond and Pearl episodes legally through the Pokemon TV app, but only up to 3 episodes at a time.
After she flees from the island, she roams the sinnoh region. Then you can use your poketch app that you use to find mesprit, and hunt it down.
You get it from a women on 1FL of the Pokemon Centre in Eterna City.