Go to Port Llast and talk to two gnome elders living in a tent there. You'll need Grobnar to make anything of the rubbish they're saying. Talk to them until your character automatically resigns and walk away - it'll turn out that they have a map to Wendersnaven Glade. Grobnar will solve the riddle it contains and you'll be able to go there - choose the Strange Clearing on your world map as your next destination.
When you're in the mysterious forest, notice the ore deposit to the right. Approach the body in the middle of the clearing and take the journal. A cut-scene will commence in which Grobnar finds an invisible instrument, the Wenderkazoo. It's a decent piece of equipment for him. Before you can leave you'll have to defeat some orcs.