Answer: Wuzu is the act of washing the exposed parts of the body. These parts of the body have been indicated to us and it is compulsory to wash these areas when we are performing wuzu. While doing so, it is essential to remove anything that prevents the water from reaching the surface of the parts which we are commanded to wash. With respect to nail polish, it is a liquid which is like that of paint and it becomes hard on the nails, thus preventing water from reaching them. As such, it will be essential to remove it in order to allow water to reach the areas which are to be washed.

And Allah knows best.
Mufti Waseem Khan