1. The Elemental Smithy is in the north of Hiberheim, right behind where you fought the Conduit's demons. It's the "altar" you mention in your second question. You either have to drag the staff onto the smithy or just use it with the party member who currently has the staff, I don't quite remember.
The barrier behind the king can be opened by using the leftmost statue on the north wall of the room. The four colored statues just give you elemental buffs that are kind of useful for the fight.
2. See above.
3. The scroll is inside the king's treasure room (see above).
