Answer a series of questions. The 'right' answers seem to vary. Some say to choose the most "evil" answers, some say to choose the last answer to each question, some say other things. The same answers don't work for everyone. Try the answers in this order: 2,2,3,3,2,1,2,1,2,2.
If you fail, he charges you 1000 Gil and suggests you try harvesting.
If you succeed, you get the quest, and he asks for one of three items. Initially he doesn't name them, just describes them.
Dangruf Stone: "The treasure I would have you seek is a precious stone. It is said to be as red as blood and found in a land of geysers."
Head down to the first large room and fall off a ledge into a room with diremites. Immediately to the left, theres a steep ramp that leads down to a spot with leeches, and a large pool in the center that looks like a Teleporter ( H-9 ).