The UUID is available when you launch an *unconfigured, unlicensed* VNS3 Controller instance.

Log in with the default username/password, and go to the "home" page of the instance.

You can reach the home page by clicking on the Cohesive Networks / VNS3 logo on the upper left of the page.

https:/<vns3 public ip>:8000/home

Then you should see something like this: