so then, something he CAN think of that can break the lock will work?
just to be clear... use sword to break off the lock, or shoot it with the whaling pistol, or imagine a hammer or something heavy that delivers a blunt blow to break the lock.
And does the whaling pistol also mean he has knowledge of how guns work?
A small, gun shaped thing (I wont doubt menen hasn't seen a gun before) that can launch a harpoon (which I also wont doubt menen hasn't seen before) from it's barrel. Not hard to imagine.
He can't make a manual or key because:
1. What is he going to put IN the manual? He doesn't know stuff about keys. Sure he may know what a manual for lock picking looks like, but not what's inside of it unless he's seen one before.
2. He'd need to see what the original key looks like to make a copy of it.