The dagger carried by the King is part of the Royal Regalia .
I don't think it exists anymore ( except perhaps in someone's private collection in the UK

) . He is wearing formal court dress usually seen in depictions of nats or other celestial beings . I guess the dagger is a representation of that used in Buddhist imagery since Bagan times .
Here is an example of a similar dress worn by a princess courtesy of the Myanmar Ministry of Culture .