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