Wheiskaet wants to give you a basic test to ensure that you are a capable adventurer.
This quest is available if you have completed the quest The Lominsan Way.
Starting the Quest
Talk to Wheiskaet in the eastern side of Eastern La Noscea to begin the quest.
Use the Herring to Lure Out the Nix
Go southeast to the quest marker. Dismount, then target the sparkling Destination, and use the fattened herring from the Key Items section of your inventory or via the icon next to the quest name in the list of active quests.
Lie in Wait for the Nix
Check on the purple glowing Destination, then kill the Inflated Nix that appears.
Deliver the Nix Leg
Swim northwest to one of the stairs and go to Wheiskaet. Talk to him and hand over the Nix Leg to complete the quest.
Next Main Scenario Quest
After you complete the quest, talk to Wheiskaet to accept the next quest: A Modest Proposal.