You can answer the question depending on what you think makes you unique. Even if it seems like you are just following trends and there are moments when you may feel like you are not your own person anymore, you have to think about things that make you the person you are.
You may be unique because of the past experiences that you have had. You may be unique because of the different people that you have met. You may be unique because of your hair or because of the clothes that you wear. Even your personality can be unique. You can think deeply and understand that your uniqueness makes you stand out from the rest.
You can answer the question based on what you think makes you unique. Do you think that you are unique because of your hair? Then say it. Do you have a hidden talent that is comical or fun to know? This is something that you can state.
No matter how similar two people look like, there will still be some differences that cannot be disregarded. Everyone is unique. You just have to know yourself more so that you can figure out how to answer this question as truthfully as possible. Uniqueness may stem from your physical appearance to your personality. Your answer will depend on you.