That key is hard to see, especially if you think 'near the goblin campsite' means 'near' rather than 'in'. From the entrance to the area head directly to the fire, and look down onto the stones encircling it.
You can jump up to the book from either side, but the side closer to the entrance would be easier. Across from about where the lone mage was, there is a small rock you can jump up onto, then jump up again to get to the book. If you jump onto the rock and keep trying to move forward, you can sometimes then jump again to get somewhere (perhaps after changing the direction you are facing, or repeatedly hitting the trigger/button to jump). Getting to the book shouldn't be too hard once you get the hang of jumping (took me a few tries); you can not get up onto the highest rock there, but I did use the forward / repeated jumping to get high enough to see that there wasn't anything on top of it.
Welcome to the forum.
