With a weaponskill of 75, a Knight can kill a demon skeleton with a Two-handedweapon and 0-2 Strong or Great Health Potions. If a Knight is using a one-handed weapon, he/she can kill a Demon Skeleton on level 30 and skills 65/65 quite easily. Just bring a few Health Potions for safety reasons.
A Paladin could hunt these with a distance level of 60. Demon Skeletons are slow, so lower skills wouldn't be a safety concern; you'd merely waste too many bolts for the loot they give. To reduce the waste, you can use Enchanted Spear, because it has a stronger attack and is hard to break. The Divine Missile spell works great against Demon Skeletons. Have an Divine Healing spell ready to use if they actually touch you.