A very easy Trophy to get as well. While progressing through Knack you will come along destructible walls, which aren't hidden very well and mostly easy to find structural changes of Walls and Rocks. Smash one of those, get inside and most of the time you'll have to follow a small path which leads you sometimes to relics or sunstones, but most of the time you'll find a treasure chest and the Trophy is yours.
The First One could already be found in the Tutorial Level's Garden section.