A Knowledge Cube is a small treasure chest that contains a building plan of a forgotten culture.
Pok can summon a new Knowledge Cube if you have accumulated enough reading power points. You do this by solving exercises correctly. The number of reading power points you need to make Pok conjure up a cube is shown in the top left-hand corner of the screen.
During the introduction, Pok already gives you a Knowledge Cube with some building plans in it, so you can already start building your camp.