I'd like to implement a kind of a tracing mechanism within IIB. Can the IIB (WMB) publish messages to a topic, using the MQ* nodes and not JMS*? I don't see any node that could do so.
If you want to use MQ topics then I would suggest JMS.
If you are using an MQTT server then you can use the MQTT nodes. If you don't have them installed on your version of Broker then you can get them here (the MQTT nodes on GitHub are not officially supported).
If you want to use MQ and are really against JMS then you can use the Publication node. To set the topic that the publication node publishes to, you need to set the property "Topic" in the messages header itself, either by setting the property in the MQRFH2 header outside the flow or in a compute node or by using the "Topic" property in the MQInput node at the start of your message flow.
Depending on exactly what you are trying to do there are also built in Monitoring Events. You can get your Integration Server to publish events to a topic automatically when messages pass through node terminals and on transaction start / end events. The topics will then be automatically monitored and can be saved in a configured DataCaptureSource database.