The Wuxi Finger hold does not exist in reality or even in mythical Kung fu scriptures.
It's a script writer's creation. But it is inspired by some real stuff like Touch of Death. It says
The 2008 animated Wuxia parody Kung Fu Panda depicts a "Wuxi Finger Hold", in which holding an opponent by one finger produces an enormous shockwave of energy.
Also, if you look into the Kunfu Panda wikia you will find this -
In a Scholastic News Online interview with "Po", when asked about the hardest move for him to learn, Po answered it was the Wuxi Finger Hold and states that Shifu told him (after having defeated Tai Lung with it) that there actually is no such move; it was just a story that masters made up to scare their students. Po added that he can't recall exactly how he did it, but he feels he must practice.