18 cases, 16 questions, 81 steps. Every step shows the correct answer.
Take the quest Identity - Case Solving
I've heard that the Enforcer's Hall has a backlog of cases, why not go and have a look?
Talk to the NPC at the coordinates above to take the quest.
Main cases of the Case Investigation system
Cases inside Mortal World quests
Cases inside the main story
Daily events while on patrol