"Report to General Kirika" "The Twilight Mystery" "Deadly Desert Venom" then turn in "Taking Back Silithus" and accept "Securing the Supply Lines"
After they're done, turn them in and get the follow ups.
These mobs are all over the west side of the zone.
Twilight Tablet Fragments spawn around this area. Pick them up.
All the mobs you need spawn all over the southern side of the zone. Be careful, though, as the south part is densely populated by mobs and it's easy to get swarmed if you aren't paying attention to your surroundings.
Return to the Cenarian Hold and turn everything in, get all the follow ups. Then start circuit 2.