Pretty much any where just look. if this does not help go on Google and put Pokemon diamond underground hikers (if u don't have diamond put which Pokemon game u have)
That simple
Be more specific please.
The hiker (in Pokemon Diamond, Pearl and Platinum) to find a Happiny will be on Route 210, South Pokemon with Breeder Kahlil.
get spheres and talk to a hiker underground
You receive it from a hiker at the Mount Coronet entrance.
the hiker is in mt.cornet
you can only find a cranidos on diamond and a shieldon on pearl
In the underground
in the underground
underground
You can sell it to that hiker guy
In the Underground.
underground