<Sir/Ma'am>, as we move through Skorn, we have to bring down those towers!
If you have a look at them, you'll notice that their tops are lined with casters. Getting too close to them would mean certain doom for us!
However, we do have it within our means to call in cannon volleys from Westguard Keep. To do so, we need to get close enough so that you can lob a smoke flare atop of them.
The towers circle the "upper" part of Skorn. Keep your distance! ~10 frostbolts can knock a player out pretty quickly. Don't stand near the tower during the strike or for very long after the fact. ~2-3m respawn on the casters.
Keep this quest open until you have finished the entire questline, including killing the leader of Skorn, then turn it in last. Unless you can fly, you will have to pass towers several times, and being able to take out the casters as you pass will make your life much easier.