Judgment

Your skills are found in the phone app that has the light bulb on it. Many skills are locked, but you can get 30 without needing any books. Once you get access to the app you should have some skill points built up. If you want to get these quickly, you can use the building eating and minigame objectives from the club Sega buildings to get SP quickly. Hug Bomb drinks from Popo Showa street for 10,000 yen a pop. you also get one from the box outside Yagami Detective Agency. The special skills have the lowest cost per upgrade. Once you obtain 30 skills the achievement will unlock.

I am unsure if the skills that are already unlocked count for this achievement.