Both destinations are served by Kandla (IXY). Since there's no flight route between them, the best way to travel is by road.
Khajjiar
Fly to Kandla (IXY), then travel by road to Khajjiar. Taxis, buses, and private cabs are available from the airport.
Bhutan
Fly to Kandla (IXY), then travel by road to Bhutan. Local transport options include taxis, auto-rickshaws, and state buses.