This place is mentioned by Oolong and Pu'ar when they reunite in Tale 8 One, Two, Yamcha-cha! It's where they learned how to shape-shift, an ability that allows you to transform into anything. Unfortunately, your strength stays the same, rendering it a mere illusion. Oolong was expelled from his school for stealing the female teacher's panties. The school's location is unknown, but it is/was somewhere on Earth.