Hi there,
Thanks for writing in.
Your staging site (eg. sub-domain) is or should be a fully functional site where you will be working. It’s the one that you will move or migrate on living so it has to be a complete installation of WordPress and other stuff.
Staging is a clone of your site, a complete copy where you can work on before you overwrite your main site by this staging site.
If you’re referring to staging site’s validation, then yes, you’ll have to add your subdomain to your license page and assign your license to it.
Thanks!