Ben's pretty spot on---the Citico/Slickrock has some of the cleanest water in the Southeast (Slickrock Creek) and some high ground balds at 5,300 feet. There's enough trails to occupy a 5 day trip. Heck, maybe I'll see you there. It's my usual stomping ground.
On the other hand, depending on where your friend is in TN---I'd recommend the Mt Rogers backcountry, Wilburn Ridge and the Crest Zone, in southwast Virginia. Dog friendly, too. It's one of the best summer backpacking destinations in the South.