it is #7
its a poketch app.
You get the Poketch Dowsing Machine from Rowan's assistant on Route 207 after getting the Bicycle. This is on Pokemon Diamond and Pearl by the way...
Your rival will give it to you sometime in the game.
Dawn/Lucas gives it to you after you beat the cycling road.
use your poketch dowsing machine which is given to you by Lucas or Dawn
use the Dowsing machine/itemfinder app on you're poketch.
i think there is the dowsing machine app for poketch at the jubilife company
I am thinking you get it from the poketech company. correct me if i am wrong
The Dowsing Machine Poketch App can be obtained once you beat snowpoint City completely. After that, prof.rowan will come on a hover craft where they finaly destroy team galactic and they pick what app to get either the Dowsing Machine App or the water tracker app.
Go to the Poketch building in jubilife and you get it some where in there.
7
The dowsing machine is on the pokewalker.