What an odd question! The use of the phrase "Don't you know it's a fashion?" (although ungrammatical) suggests that the speaker thinks that the other person "should" wear slippers to work. However, starting it with "Amazing!" makes no sense. Are those lines meant to be spoken by two different people? If so, the whole dialogue is nonsensical. In my opinion, it's a terrible test question.
The only ways I can make understandable dialogues of any parts of that question are:
Jane: Amazing! You wear slippers to work!
Sue: Yes, don't you know it's the latest fashion?
Jane: You should wear slippers to work.
Sue: Should I? Why?
Jane: Because it's fashionable.