It is located in Innoventions West, which is the Innoventions building on your right when Spaceship Earth is behind you.
It's inside the first part of Innoventions near a Segway Tour attraction and a bank of video game consoles. The Visa area is behind a black curtain and there is a short queue area.
The second part of Innoventions West contains the Epcot Character Spot which is open to anyone. It's different from the Visa characters meet and greet.