Is there an airport in Nong Khai...i don't see any commercial airlines flying there...

Nope - Udon Thani is closest with about a 30-40 min drive

Vientiane is a bit closer, but in another country....

There used to be, now a cluster of government buildings built on the site.

My first commercial flight in Thailand was out of Nong Khai on a Thai Airways DC-3 over to Nakhon Phanom, the old commercial airport right down close to the Mekong, also long gone, overbuilt with government buildings.

Mac

THE airport to also serve NK is obviously Udorn Thani-with plenty of flights on various airlines to BKK and even the odd flight to ChMai on NOK. Direct minivans await you after flight-most use them to go to Lao-bridge, but (do I really need to tell this?) they can also put you down on the point where the main road enters NK-township. Just ANY guidebook or a very short look on any decent map would have told you the same without the bother to post and wait for an asnwer-incl the tipical TV memories from years ago