Did you check your journal? it should help you see what you need to do for your next step. I believe you are to the point where you go into the instance dungeon and have to fight 3 boss mobs to complete your quest.
Go to Darkness Falls entrance. Try to /use the wayfinder amulet there. It should port you into a dungeon. Depending on what type of toon you play, you probably won't be able to solo this whole dungeon yourself. The final mob lifetaps you, so unless you can dish out serious damage, you will need a buddy or two.
btw, Onnolo is at the entrace of this instance dungeon...once you port in, you won't be able to miss him.