As the description of the achievement suggests, you need to be in Fossil Roo in order to get this achievement.
As you make your way through the place, talk to the miners, until you find the last one that will ask you if you are interested in excavating. Accept and walk to the top part where you will see a number of loose rocks. Tap away at the rocks until you hear the cries of Kuppo inside a skull, trapped underneath the rocks.
Once Kuppo jumps out, the achievement is yours.