How many times do most students surf the Internet a week?
或：How many times a week do most students surf the Internet?
我本来是一楼,但是二三楼答案有误,怕误导楼主.
如果是对two or three times a week一起提问,才是：How often do most students surf the Internet?
而单独对two or three times提问的话,则用How many times做疑问词.