Each trophy piece is awarded when a group of six levels are completed (no medals need to be earned). So, you get this for beating the fourth set of six levels (19-24) in Apprentice. The levels are easy, but if you have any difficulties, you can consult my step-by-step solution for each level here:
http://glowartisan.4shared.com/ or here:
http://sdrv.ms/HEiHyAThere is a spreadsheet there, and it has tabs for each of the difficulty levels. Color outlines/numbers show you which order to draw the colors in.