Bangkok Suvarnabhumi Airport caters for both international and domestic flights, while only domestic flights are catered for at Don Muang Airport. Journey between the two airports is an estimated 1 hour (or longer depending on traffic conditions), so give some time buffer should you be required to switch airports for a connecting flight.
There are daily direct flights from Hong Kong to Bangkok, they are Cathay Pacific Airways , Thai Airways, China Airlines, Hong Kong Express Airlines, SriLankan Airlines, Kenya Airways and Royal Jordanian Airlines. ZUJI Hong Kong provides cheap airfare to Bangkok available with instant confirmation.