How can I find my personal endpoint in AWS IoT?

I'm trying to write a Java app that behaves as a Thing, publishing data in AWS. The Documentation has this code sample:

String clientEndpoint = "<prefix>.iot.<region>.amazonaws.com";       // replace <prefix> and <region> with your own
String clientId = "<unique client id>";                              // replace with your own client ID. Use unique client IDs for concurrent connections.
String certificateFile = "<certificate file>";                       // X.509 based certificate file
String privateKeyFile = "<private key file>";                        // PKCS#1 or PKCS#8 PEM encoded private key file

// SampleUtil.java and its dependency PrivateKeyReader.java can be copied from the sample source code.
// Alternatively, you could load key store directly from a file - see the example included in this README.
KeyStorePasswordPair pair = SampleUtil.getKeyStorePasswordPair(certificateFile, privateKeyFile);
AWSIotMqttClient client = new AWSIotMqttClient(clientEndpoint, clientId, pair.keyStore, pair.keyPassword);

// optional parameters can be set before connect()
client.connect();

I know what clientId is and how to find my ID, but I cannot understand the in clientEndpoint.

It's not the account's personal endpoint, but the Thing's endpoint.

Go to IoT Core -> Manage -> Things, select your thing -> Interact. Its the URL under the HTTPS part. It should be in the form xxxxxxxxxxxxxxxxx.iot.region.amazonaws.com, where the x's should contain mainly lowercase letters, and maybe some numbers.