wuut is simply wuu2 which we all know means "what you up to". This has been changed because now not many people type using numbers anymore :)
This technique can also be used in say wubu2-wubut and others similer
> one: heya x
> two: alright babe?
> one: yeah taa, youu?
> two: good, yeah thanks. wuut?
> one: on urban dictonary. youu?
> two: sames!!!