It is sitting beside the fire, on a rock, in the goblin area. If yours isn't there after mind reading it might be a bug?
I wouldn't stress about the chest too much, since chests are level dependant you will usually get about 5-12 gold [that's what I've seen it have] and if you are really lucky, or save/load a bunch, an average weapon that you will replace about 5 minutes into the game.
Get the skill book and continue playing the game, the chest has nothing important. If you really want I will start a new game and screenshot the key - if you can't find it from my description.
