Thanks everyone!
In the case of other terrestrial lizard species and snakes they lick to take scents from the ground and air and transmit them to the vomeronasal organ on the roof of the mouth directly. So essentially they are smelling their environment. It's brought up in a previous thread that panthers are often seen doing this behavior, but not veileds. There were a few other species (I want to say carpets and oustalets, but don't quote me on that) lick as they explore also. Both of my panthers do it, but I've never seen my veiled or Jackson do it.