Depending on what you like, there are some good places in the Kingsport/Tri-Cities Area if you're willing to drive around and look for them (I lived in Kingsport 20 years and still get lost)...One place I like for a simple breakfast is Kaddy's Korner - the best ambiance I've ever had in a breakfast restaurant. It's a couple of older ladies short order cooking typical breakfast foods. It's simple, good food - nothing fancy, but a lot of fun to go in there and cut up...a Kingsport classic.
If you're in the mood for seafood, a lot of people would recommend the Riverfront Seafood Market. It's OK; probably the best seafood you'll get that far inland. Sitting by the river can be good or bad; when I went, there was a lot of garbage washed up on the shore and it smelled terrible because the wastewater treatment plant is less than a mile down the road.
Troutdale in Bristol is good...Cafe Pacific in Johnson City/Pacific Grill in Kingsport are supposed to be good, but I haven't been to the new location. It's probably the best Asian fusion in the area. Cootie Brown's is decent; interesting drinks but I would say the entrees need a bit more refinement. The Parson's Table is excellent, but I'm not sure if it's still open. If you're looking for Q, you could try Ridgewood BBQ but they are notorious for never being open.
You have to try Pal's...it's a local fast food chain, lots of fun too.
If you like a particular chain restaurant, chances are you'll find it in either Kingsport or Johnson City...but there aren't as many unique local restaurants as I'd like. It's ironic, Kingsport used to have a really good local restaurant scene in the 80's/early 90's but people complained that we didn't have the big chains like Johnson City.
Enjoy your time in Kingsport...hope the acetone scent doesn't destroy your palate.