There seems to be a bit of a trend with the Nornir chests in God of War Ragnarok where two of them are fairly easy to find and the third one is difficult. The Nornir chest in Raiders Hideout is a strong example of this. You will find two of the braziers needed to unlock this chest quite close to the actual chest. The third one is nowhere to be seen.
Depending on the type of screen you are using, this one may be one that you miss as it is very far away and you will need to make use of those exploding balls to be able to light it.
There is a little pot that provides an infinite supply of explosive grenade items. Pick up one of these and turn around, walking toward the entrance you came through. There is a large pit to the left. If you look down here, you will notice a brazier in the far distance.
You won’t be able to throw the grenade item directly at it as you wont be able to get the arc but try your best. You will see where this explosion hits and from here, you can use sigil arrows to bring that explosion from where the grenade hits up to light the brazier and unlock the chest.