In order to meet Chark, you need to go to the shining blade camp from Temple of the ages, exit out through the Black Curtain and follow the path. Enter the camp and listen to the first dialog, then exit the camp, turn right and zone out (no enemies). Come back and listen to the 2 subsequent dialogs before going Vlox's Falls. Meet Chark outside in Arbor Bay. If you don't listen to all 3 dialogs you have to start over.
"I am looking for witnesses in an upcoming trial. Were you involved in the R.O.X., P.O.X., or N.O.X, incidents?"
"Yes, and I have M.O.X. to prove it"
"In that case, by the authority of the arcane council, I officially request your presence at the trial of Zinn. And when I say "request," I mean "command." It is the arcane council after all.
"I don't know anything about those"
"Well, today is your lucky day then. You'll have the opportunity to learn all about it. Fascinating stuff... intrigue, drama, wanton destruction. You'll really enjoy hearing the story. If anyone asks, just say you're a "witness." After all, you are there to witness the trial, so technically, it's true."
"No, I've heard about them though"
"Excellent, excellent. This is an ideal opportunity for you to learn more and to share what you've already heard. Rumours and hearsay are the foundation of any good court case!"