When I make a Mage I put points into Int, Will, Dex and Con and Dex + Int would work for a Knock spell with the chance of failure or a Critical Failure depending on how many points you place in stats or it just say's your skill isn't high enough to unlock this chest.
Coarse all this could be solved if you play a Mage or Fighter and have a Rogue follower at the start of the game, in DA:O in the Dwarf Noble campaign you get a Rogue but he doesn't have lock picking, At Ostagar in the wilds you get Daveth a Rogue no lock picking, while I understand there's junk in the chests But I see it I need to unlock it.
The only consequence I can see if you don't have a Rogue in the party to unlock that chest is the Mage casts a Knock like spell and crit fails fubaring the lock, the fighter steps up to break the lock and ends up smashing the chest and breaking some or all the items thus the importance to bring a Rogue instead of sending him on that Intelligence gathering mission.