When a frame enters a switch, the switch will take the source MAC address and update its MAC address table with the interface where the frame entered the switch. That interface can be an access or trunk interface.
Broadcast or unknown unicast frames will be sent to all interfaces (except the one where the frame entered the switch), including access and trunk interfaces.
Known unicast frames will be sent to the switch interface indicated in the switch MAC address table, whether an access or trunk interface.