Make sure that JMX is enabled in ActiveMQ. For more information, see ActiveMQ - JMX.
ActiveMQ provides a publish/subscribe mechanism to relay node events from the repository to the Sync Service. The JMX beans that exposes information on the node events topic is:
org.apache.activemq:type=Broker,brokerName=localhost,destinationType=Topic,
destinationName=VirtualTopic.alfresco.repo.events.nodes
The Sync Service consumes from a queue that is tied to the virtual topic. The JMX bean name of this queue is:
org.apache.activemq:type=Broker,brokerName=localhost,destinationType=Queue,
destinationName=Consumer.<SyncId>.VirtualTopic.alfresco.repo.events.nodes
where <SyncId> is a UUID that uniquely represents the Sync Service. This UUID can be obtained from the Sync Service health check.