WoWDB

If you are camping this guy, you might need to manually add him to NPC Scan:

/npcscan add 64004 Ghostly Pandaren Fisherman

Located in a small indent with some shallow water, on the north side of Cattail Lake. Interact with him, and he'll give you a dialogue option. Be warned: If there's someone else there, you (the persons) will need to coordinate clicking the dialogue option because the npc disappears immediately after selection. I managed to do this with my twin, and we both got  Ancient Pandaren Fishing Charm.