UDP supports multicasting and broadcasting in transport layer or application layer? We know that UDP does supports multicasting and broadcasting. My question is which layer "UDP supports multicasting and broadcasting"? Is it transport layer or application layer? We know that in application layer multicasting possible and it's correspondence multicast address also exists. But how is it possible application layer broadcasting?

Multicasting and broadcasting are at lower layers than UDP. UDP is used as a transport protocol for multicast and broadcast because it is connectionless. You could use any connectionless transport protocol, but NAPT has limited the IPv4 Internet to TCP and UDP, but TCP is connection-oriented, so it will not work with multicast or broadcast.