"What the dog doin?" is a term often used to describe utter confusion of an act that the canine seems to be committing. The dog could be walking, peeing, shitting or generally doing what a dog does. Though, people tend find themselves holding back from saying "what the dog doin?" when seeing a dog doing something rather mundane.
A: "Yo look! what the dog doin?" - "he acting a bit sussynowinnit?"
B: "he's just pissing.."
The dog is usually performing a human-like task. e.g. Kickflip, playing GTA V, eating squirrels, playing a nice game of CS:GO, and playing piano. Dogs are fully eligible of doing all of these human tasks. If you as much as lay finger on a dog, it might initiate god mode and use 0.1% of its power. A dogs full power is so powerful that it can take down an entire solar system effortlessly. The average house dog is currently using -0.0000007% of its current power. 0.1% is enough to wipe out the entire country of Uruguay. So remember, do not mess with a dog, or you will find out what the dog doin'.
(You see any being perform or say something weird) What the dog doin'?!