KTM, Kathmandu, is the only international airport.
The Star Alliance booking tool is helpful here (www.staralliance.com). Just start a round-the-world trip in Kathmandu and look for the dark blue dots. Thai Airlines seems like your best *A bet; it flies from BKK daily. Another option is Air China, which returns from KTM to PVG through Chengdu on Tuesday and Saturday. But Thai and Bangkok have more options.