Berek's Grip Leeches One Shot Enemies??

Erm so if I wear 2 of these and get Ghost Reaver do I get 4% ES leech against enemies that I shock/shatter in one hit?

Ghost Reaver would turn all of your Life Leech effects into Energy Shield leech effects. So yeah, with two of those on, whenever you will hit an enemy who is both Frozen and Shocked, you will have a 4% Damage leeched as ES. Even better to boost with an Energy Leech support

No, if you one-shot an enemy they will be neither shocked or frozen when the hit lands = no leech. Unless you are applying shock/freeze via non-hit methods you'll never leech on the first hit with that ring.

Right, question was about oneshotting an enemy, not killing it.
While indeed if you kill an enemy with a very high lightning damage you might see a shocked corpse, remember that ailments are applied before hit. So, you haven't "hit" a shocked enemy - because it was not shocked when you oneshot it.

If you need to pre-shock an enemy in order to oneshot it, you might use Storm's Gift + Inpulsa, or just Skitterbots. Freezing without hitting is, however, something only an Occultist can do, and only so many times per second

well thanks guys that explains why the ring is so cheap - it's not exactly easy to freeze bosses consistently and everything else is basically one shot so the leech on this ring is a bit of a tease