Get List of Unlinked GPO's from Domain.

Below Powershell commands will give the list of all Unlinked GPO's from a domain.

$unlinkedGPOs = Get-GPO -All | Where-Object { $_ | Get-GPOReport -ReportType XML | Select-String -NotMatch "<LinksTo>" }

$unlinkedGPOs | Sort-Object -Property DisplayName | Select-Object DisplayName,CreationTime,ModificationTime | Format-Table -autosize