A dagger that banishes level 12 daedra.

My character is level 35.

How do I know, or is there a list of...

what is a level 12 daedra?

I've been wondering this myself (not just Daedra, any enemy level).

I usually just leave items like this where they are. Useless to me.

My knight in Oblivion just retrieved Mehrunes', albeit at terrible personal cost. So, my character in Skyrim is naturally intrigued by this.

Where did you find it?

http://www.uesp.net/wiki/Skyrim:Daedra

It will kill Flame Atronach in on hit, however at level 35 they should be easy to kill.

Daedra is rare in Skyrim making it pretty pointless, like a weapon with bonus against Khajiit.

Keep or disenchant the dagger dont sell it, its useless in combat but nice if you want to train enchanting as the banish enchant pays very well.

I found it on this bandit reaver guy in Solthstheim, when I had to go there for a crossbow schematic.

Ok. So just the flame daedra?

Gonna toss it then. Flame atronachs don't even get close to my character. Two elven arrows is all it takes. Thanks.

Random loot probably.

The uesp only lists Daedra at level 1, 20, and 30 for Flame, Frost, and Shock Atronachs respectively.

At least you found yourself a good way to make better money.

There is not one. Basically, this will banish Flame Atronachs, Frost and Storm are higher levels.

http://www.uesp.net/wiki/Skyrim:Daedra