You can spell it out our just pronounce it the way it is. This stands for the saying ”what u talking about willis,” from the show Diff'rent Strokes. It was usually said by Arnold (Gary Coleman) to Willis Jackson (Todd bridges).
Ben: Hey Dan remember when we went to vegas and went to every strip club in the city, that was fun!
Dan: What u talking about willis? (Wutaw)
Debbie(Dans girlfriend): Yes Ben please give more detail about what happened so Dan can remember...
Dan: I am in trouble ain't i?
Debbie: Ya think