If you are in sneak mode, you can get close enough to the DK to fire an arrow or 2, and then run away a bit... Initialy this wont look like its doing much... because they CAN heal themselves (but only 3 times IIRC), so eventualy you get their health down, and then attack them with melee / magic.
after you killed the first DK.... go to your quest screen, click on trophies and check what they are the least immune to...
then use THOSE type of arrows on the next one you try to kill with this method.... it will make a HUGE difference...
