Explanation
You can use the Get-MsolUser cmdlet to generate a report that lists all the users who completed the Azure MFA registration process. The full command would look like this:
Get-MsolUser -All | Where-Object {$_.StrongAuthenticationMethods.Count -eq 0} | Select-Object -Property UserPrincipalName Reference:
https://docs.microsoft.com/en-us/azure/active-directory/authentication/howto-mfa-reporting