Linken, in case you can't find him, is inside the tree hollow tree trunk in front of the cave and the flight point, and to the west of Larion the dwarf. 

In order to get the quest from him, you have to find the raft, which is in the south east part of Un'Goro, in "The Marshlands", on the west-ish bank of the most south-west lake.  If that made any sense.  There's a raft there you get the quest from, then you dive down in the lake to get the bag of stuff, then you bring it to Linken in Marshall's Refuge.

you dont need to find him... if you have the wrecked raft stuff, he'll show up on radar for finishing the quest... if you want to find him before you start the quest... im not gonna finish that