How can I see what destinations are used
The easiest way is to use JMX by pointing your JMX console or JConsole at the broker JVM.
You can also get all of the active destinations from the broker using Java code via getDestinations().
You can also get a Map of all the Destination objects indexed by ActiveMQDestination via getDestinationMap(). This allows you to look at the individual destination details such as the queue depths and so forth