你不知道这是谁的毛衣，你应怎样问别人？（英文）

楼上说的有误，who`s sweater? 的意思是：谁是毛衣？
正确的说法是：Whose sweater is this?
如果你想问正在旁边的人，可以说 Is it your sweater? (这是你的毛衣吗？)

Is this your sweater?
Whose sweater is it?
What's the owner of the sweater?

who`s sweater?