Max Trinidad shows how to install Powershell Core on Windows Server Core:
In the following Virtual machine scenario, I got one Server Core with Active Directory (Build 16299) and Windows 10 (Build 16299) joined to my new domain. Both Build 16299.
On my Windows client I create a shared folder named “SharedFiles”, where I copy over the latest MSI version of PowerShell Core “PowerShell-6.0.0-win-x64.msi”.
Then, on the Server Core I’m going to create a map drive to my Windows client shared folder to then run the MSI installation from Windows PowerShell Console.
He also shows how to uninstall Powershell Core, should you wish.