Elves, being inherently magical and good creatures would probably know what to look for in assessing an opponent to determine what magical or divine protections surround them. It wouldn't tell the length of the protection, or even what level, what sort of spell etc was there, but it would give insight into what was out there.

Effects:

Let's say your fighting BillyBob, and want to use your inherent elven senses to try to figure out what's going on with him. Billy bob has sheild of winds, protection from heat/cold (Druid Spell)), and endure (Assassin skill) up (Really odd scenario, but bear with me).

inherent 'determine protection' BillyBob

What you see:

You sense invisible winds swirling around BillyBob that keep air away from him.
You sense an aura of heat surrounding the form of BillyBob, protecting him slightly from the cold.
You sense an aura of coolness surrounding the form of BillyBob, protecting him slightly from the heat.

Restrictions: That's it, you wouldn't notice endure, because that's a skill and not magical in nature. Likewise, if you're a lower level than the spell that's been cast, you would have a harder time determining that it's present, if being able to at all, in the same vein as improved invis. As well, you could limit the amount of protections you can see perhaps. Let's say someone's got the max amount of invoker shields up. Maybe the only ones you could see would be air, ooze, and earth, but you miss the other ones. If you were to look again, that would chage. Also, there'd need to be the appropriate amount of lag based around the skill.

Flame away...