Read device data via MQTT

Hi Cayenne community! I have a device that via LoRaWan is writing data through to Cayenne. I’m trying to develop an application on a Docker container that via MQTT can read this data of the device.

I’ve studied the documentation of the MQTT API and I think that the topic to which I should subscribe is the following: v1/ username /things/ clientID /data/json

What is the username that is referring? The username of the Docker container?
What is the clientID that is referring? I would say that is the clientID of the LoRaWan device, but I don’t have this king of information. Where can I fetch it?

When I connected the LoRaWan device, there was no clientID indicated.

I anyone could help me I could move on but now I’m stucked looking for this clientID info.

Many thanks,