Your employer must offer you time off on 11 November each year in recognition of your service. Whether the day is paid is up to the employer. An employer can only refuse if they can show that granting it would cause significant economic or operational disruption or undue hardship, and if they do refuse they must give you another day off before the next Veterans Day, on top of any other time off you would otherwise get.
Give your employer written notice and proof of service, such as a DD214, at least 21 days before 11 November. Your employer has to respond at least 14 days before the holiday.
Your DD214 or other proof-of-service documentation.