KnifeOshon is based on the japanese game "Azarashi". The goal is to throw a knife on the falling spiffy monster as soon as you see it falling... the faster you are, the more points you get.
I don't have a wii u anymore to test it myself, but if homebrews are not visible on the wii u menu I think you can press L + R + minus to open the plugin menu, there should be an option called "homebrews on wii u menu" or something similar