In the second RoboKing level, there is a Royal Present on the table that you start on. Roll around until you're big enough to pick up the items on the table (I believe I grew three "levels" before I could pick up anything on the table). Next time you play a level press L1, then X and take a picture. When you're done go to your "Katamari Collection" to view the picture. The trophy will unlock when you exit.