MQTT topics are ephemeral in that clients simply specify them in publish and subscribe operations. The service does not provide APIs listing topics that your clients are currently using. For reserved service topics defined by AWS IoT services, you can refer to https://docs.aws.amazon.com/iot/latest/developerguide/reserved-topics.html

Thanks. Regardless of the list of topics, which client or package do I need to publish and subscribe?

I'm a bit confused about the AWS client in general. There seems to be a 1.x version and a 2.x version. I assumed I should use the 2.x version, but most of the examples I can find don't work; I think it's because they're written against the 1.x API. What should I do?

You should favor 2.x version. Which AWS IoT SDK are you using?

You may use IoT Java Client Library. Here is the sample code:

import com.amazonaws.services.iot.client.AWSIotException; import com.amazonaws.services.iot.client.AWSIotMqttClient; import com.amazonaws.services.iot.client.AWSIotTopic;

public class MQTTTopicList { public static void main(String[] args) { AWSIotMqttClient client = new AWSIotMqttClient("<AWS IoT endpoint>", "<client id>", "<AWS access key>", "<AWS secret key>"); try { client.connect(); for (AWSIotTopic topic : client.getTopics()) { System.out.println(topic.getTopic()); } } catch (AWSIotException e) { e.printStackTrace(); } finally { client.disconnect(); } } }