You probably had task to license some server or client PC that is not domain member and besides that it is not using your domain DNS server. As you already know, KMS server is usually installed on domain joined server. So what to do? First open hosts file (%windir%\system32\drivers\etc) on computer you want to license, and add host record for your KMS server (vmo-aaa in my case).
After that you need to run two command. You need to know on which port your KMS service is working. Default port is 1688. With first command you tell client which server and port to use for licensing, and in second you activate your license. That is all you need to activate your Windows license.
Slmgr /slms vmo-aaa:1688 Slmgr -ato