From this point forward you can be on any job to finish this quest. Change jobs in Nashmau before spawning the monster if you wish.
Exit through the east gate of Nashmau. Head to the east side of the lake at (I-10) and cross over lily pads to reach an island with a ???. Click on the ??? to spawn a notorious monster called Caedarva Toad.
Defeat it and check the ??? again for a cutscene.
If you zone before checking the ??? for the cutscene you must fight the NM again.