I think you need Know Creature to show the NPC's level.
Know Creature (Passive)
Know thine enemy. This skill grants you insight into the strengths and weaknesses of your opponent. While initially this skill might not look so appealing, it is definitely worth investing to, as it might give you the key insight into how to kill an enemy which seems to be resistant to whatever you do.
Level 1 Succesfully identify monsters up to level 10. Shows the hitpoints of the monster.
Required level is 3.
Level 2 Succesfully identify monsters up to level 20. Shows damage and armour of the monster.
Required level is 7.
Level 3 Succesfully identify monsters up to level 30. Shows offence and defence of the monster.
Requireed level is 11
Level 4 Succesfully identify monsters up to level 40. Shows the chance to hit, hearing and sight of the monster.
Required level is 15.
Level 5 Succesfully identify monsters up to level 50. Shows the resistances of the monster.
Required level is 19.
