In Highpass Hold:
Shares spawn point with Grenix Mucktail.
You can find him at /loc 815, 105, -99.
There is also another static spawn near him by the tree just as you go up the slope to his location.
Additionally there are 2 roamers which will walk up the slope as well so be careful if camping him while the gnolls are still within EXP range of you since they will run up and may aggro you just as you are fighting Vexven.
If you don't want to bother with killing the gnoll placeholders and roamers, and you have non-KOS faction standing with the guards, then you can just kite all the gnolls to the guards and have the guards kill them for you. This way you get rid of them quicker if you are just after the named spawn.