1 GATE QUEST 1:
You can find this mob at both Xiamen -Main Gate- and Xiamen -Exit-.
After that, you can move to Xiamen at the other side of the gate when you talk to the guard.
(Don't go to the south into Xiamen. It's a dead end since its on the left side of the gate)
2 GATE QUEST 2:
This next part of the quest is at Yellow Gate -Main Gate-. Talk to this NPC Guard:
He will ask you to bring him 50 Yellow Mana Gems:
Which drop from this mob:
This mob can be found at Craving Basin -Entrance- and Yellow Gate -Main Gain-.
Congratulations! You can now proceed to the maps beyond Yellow Gate!