Q: What has attacked my fringe tree? I am hoping you can help me decipher the problem.
A: The damage along the midvein indicates some sort of piercing/sucking insect.
I think your tree is hosting a hungry population of fringe tree lacebugs. They are not terribly common, but have also been observed on ash trees and lilac.
The most effective control for lace bugs is a systemic insecticide like imidacloprid (click for sources). If you decide to go this route, apply the insecticide after the tree finishes flowering so it does not harm pollinating insects.
FOLLOWUP: You were right! I was able to take some closeups of the bugs on the back of the leaf.
(The black specks on the backside of the leaf are exactly like what I’ve seen when lacebugs attack azaleas.)