Summary: Use Windows PowerShell to find the dates of the last Windows Defender scans.

Hey, Scripting Guy! Question How can I use Windows PowerShell in Windows 8 to find the dates of the last quick scan and full scan
          from Windows Defender?

Hey, Scripting Guy! Answer Use the Get-MpComputerStatus cmdlet and select properties ending in the word age:

Get-MpComputerStatus | select *age