Correct me if I'm wrong (and I may very well be), but I assume you mean the finger position "shocker" and not the basic idea of shocker to a girl such as, waking up bald, or on a prison ship headed to Siberia or next to your long deceased Aunt Betty-Anne.
But I digress, the shocker, performed on a woman, administrated by a man or woman, involves inserting your index and middle finger into a woman's vagina, folding in the ring finger and inserting the pinky into the anus. I suppose the "shocker", in reality, is the pinky. Sort of like, "Lah-di dah, la la, I'm getting fingered and oh man what's that? Wow! Now I'm getting simultaneously fingered in the ass - That is a shock."
Also, the shocker hand position itself is much more popular than actually administering it. It's sort of like a surfer Hang Ten hand thing.