You phrased the question weirdly. What you should've asked is how much power does the WiiU use in Standby, since that's what you want to know - it obviously takes power, you can see the light.
The WiiU is powered by a 75W power adapter, during standard operation it takes less than a half of that amount. When in Standby it takes 0.22W, this power is used for the fancy light as well as for staying connected to various services.
The WiiU also has no Spotpass - nobody's going to go around with their WiiU in their backpack and
"Pass" by anyone else doing the same thing - you were thinking about Nintendo Network, julialy.