Speak to Shyla Starhearth at (7423, 3130) in Sanctum or Sylver Valis at (6205, 5196) in Merdian to begin the scavenger hunt after completing The Great Scavenger Hunt, Part 1. Find a task master in each of the challenge zones and complete their quest! Check the individual subquest pages for walkthroughs of those quests.
This quest is only available during Phase 2 of the Summerfest event.