Solved: (I'm not certain this is the same across all deployments) the Server Url is https://xxxxxxxxx.crm.dynamics.com/ where the "xxx" is the unique Environment ID that you are given in a CDS v2 environment.
Thanks for the info. I spent (what seemed way too long) to transfer my entities and apps to a new CDS v2 environment. It seems the import/export is not fully functional but that is to be expected.
So I'm still lost as to what Url I input in Power BI when on this screen. The App URL does not give me anything so is there a server address that I'm totally missing?