There;'s a difference between doing and singing. So widely said is singing karaoke. I am doing my homework or playing ball. Maybe think doing as general action as most would understand doing karaoke.

I don't think that KTV is used as a synonym for Karaoke outside of China - certainly not in the west, so if you want to be understood by a wide range of people, don't use that abbreviation 'Singing' is probably more natural, but 'doing' would also be understood.