Q.Wild Fox Grape Vines
I have some wild fox grape vines growing up a tree about 30-40′. They have lots of grapes each fall but are hard to harvest. We built an arbor near the tree and want to pull the vine down from the tree and put it on the arbor. How far back should I prune the vine? It is about 20′ high before the first fork in the vine with no shoots on it – just a hardwood vine.

Certified GKH Gardening Expert
Prune back the vine to a manageable size. This article should help you with continual pruning care in the future: https://www.gardeningknowhow.com/edible/fruits/grapes/prune-grape-vine.htm