Probably China. They are the biggest player of bitcoin for many years. I think they are also the biggest bitcoin miner as far i know. The next i think US but there are problems regarding on the legalization of bitcoin there. Maybe Japan can surpass US or even China due to massive adoption of bitcoin there. Many establishments there are now accepting bitcoin. Bitcoin growth there is phenomenal.
I don't think so, After regulating on the ICO market Chinese people got discouraged to be engaged in this system. day by day this place has been taken by the United State's people. they are using Bitcoin for many purposes, Normally they are spending Bitcoin for their Breakfast, lunch and Dinner order. they also spending Bitcoin on various types of shopping.
Not only that Bitcoin trade much appears at this location.