Hi,
Thanks for the interest in our plugins. I can answer your questions.
The license is done per install of WordPress and not by domain or subdomain.
So it would be two sites.
However, the license is only needed for Automatic Updates so you can use the license on the live site and then just manually update the dev site.
Or reverse that.
We have more license related guides here:
https://theeventscalendar.com/knowledgebase-category/purchase-install/
Including how to move license keys around.
Let me know if you have any follow up questions.
Thanks