Are you asking how to make a latex prosthetic in addition to giving it an outer layer of sand? Or are you just asking how to get the sand on the prosthetic after it has been made?
There's not much to putting sand on a latex prosthetic. Just brush a layer of latex over the surface and then coat it in sand. It's just like making art with glue and sprinkles in kindergarten.
If you're asking how to make the prosthetic, I'd need to see ref photos to give you advise. They range from easy things that can be done in under and hour, to complicated multi-piece prosthetics, that take hundreds of hours before the first one is cast.
A sand coated glove is probably going to be a bit messier. As you move your fingers, the glove will rub against itself, causing some of the sand to be scraped off. This isn't the end of the world, just keep it in mind.