There isn’t one at Knox. They hauled off almost all the historic armor from the Patton Museum to Benning several years ago, with the idea that a new museum would be built there for it there. Hasn’t happened yet. It’s all sitting in warehouses (best case) or outside (hope not).
The museum is coming.
https://www.armorcavalryheritagefoundation.org/museum-1
Projected opening date is in 2022.
Failing that, there is a Russian T-72 on display at the Canadian War Museum in Ottowa, Canada. There was another one at the Aberdeen Proving Grounds’ Ordnance Museum but that museum has been moved to Fort Lee. There’s an Iraqi one in Danville, VA at the American Armor Foundation museum.
The Bovington Tank Museum in the UK and the Australian Armor Museum also have T-72s inside on public display. Here’s a video of the Australian one.
https://www.youtube.com/watch?v=krp2y88nNCo