I've been granted access to the Teeth of Naros by a strange entity that claims it brought me here. I'm supposed to "seek the Primos." I should see if there's some way for me to find out what this means.
The easiest way to kill him is to take out the two Kobolds behind him, which will lower his damage resistance and prevent him from regenerating health. On the PC version, after killing both Kobolds they can clone one at a time.
However, killing him while leaving the Kobolds alive earns the achievement "The Harder They Fall. (This may only require leaving one alive, at least on PC.)
The Fateless One can decide whether to kill or spare the remaining Jottun (this only changes some dialogue and has no impact on future events).
There may be a small impact, if you spare the Jottun here and also rescue the slaves in The Perpetual Desolations quest, the Jottun become peaceful NPCs afterwards and cannot be farmed without going criminal.
She will also give you a primal weapon (Primal Mirror for example).