What do you think the white/silvery thing is between his hand and his shoulder, though, if not a sword? You can also see the other side of the sword's handle on the bottom left part of his right hand.
He's reaching behind his back with his right hand, not holding it up to grab something in front of him. The part of the trident that looks attached is just the crossguard of the sword.
It's a pretty poor pose to do for concept art because so many people have misinterpreted what the picture is actually showing, but I'm certain that he is holding two weapons there.
A scroll, a scroll support or a thingy in which you put a scroll to preserve it. I don't know how that's called in english. I don't even know how that's called in my own language
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You can see that there is a white circle on whic there is a conic shape. Somethin like this but more simplistic. There is also a darker one under it and you can see its ending on his lower left. It seems to have a cylindrical shape ( at least to me)

Even in the "War Room" concept he has some smaller scrolls, but those are hard to see. Look at his left foot.
I think that they were still playing with his looks when that concept art appeared in the companion leak.
EDIT
Here's the pictures again so that you and all the other people might easier see what I'm talking about.

