Question: I have several 2 year old muscadine vines that are producing well. The vines hang to the ground. Am I supposed to keep the vines pruned back off the ground?
It doesn't hurt anything for the vines to hang to the ground. They may get in the way of your lawn mower. There's also the greater possibility for them to be sprayed if you apply herbicide under the vines to kill weeds. Other than that, there's no harm in letting the vines grow to the ground.
On the other hand, if you wish to prune your vines to tidy up a bit, it won't hurt them in the least. I suggest you prune them so that they hang no lower than your knees. I'm assuming that you are growing them on a single wire trellis.