It's not exposed in any cmdlet that I know of, and it doesnt look like the user entity in Graph uses it either.
How to get countryLetterCode from Azure AD
I was trying to retrieve the attribute that is mapped from the "c" attribute in on-premise AD to Azure AD. The attribute seems to be called "countryLetterCode" in Azure AD.
But I cannot find a way to get this "countryLetterCode" attribute via PowerShell. I've tried the followings.