( )do you go shopping every week?-------Twice .

( How many times)do you go shopping every week?-------Twice,
你每周去购物几次?--两次.为什么不用how often因为前面的问句里有every week,how often的问句里通常是没有这种事件的表示的，比如：How often do yu go shopping?--Twice a week.