For the people of Calpheon (Citizens of Calpheon) knowledge, the one you want is on the road between Delphe Outpost and Delphe Knights Castle. The road goes along the top of the mountain. He is at 240m from the outpost and 360m from the castle.

Adding a note here. I ended up at Karanda Ridge where there is also a Clarkster who's a node manager. If you do end up there and you're not gaining any knowledge, then it's the wrong Clarkster and make sure you're at the correct place as identified by the pictures in the previous comments.