The most common way to handle this will be rubbing compound and preferably a power drill or buffer. If this is a tail light it is likely a plastic of some kind. You can polish out minor surface scratches with rubbing compound and a buffing wheel.
This of course depends on if this is a scuff or what most would call a scratch. If the depth is significant there isn't much you will be able to do. If it isn't places like Jiffy Lube offer a relatively quick and cheap polish surface for dehazing headlights that may be sufficient. Or, your local auto parts store likely sells a kit designed for the same purpose that could work.