How can I locate my MS Office license key?
From Microsoft.


Launch application and click Enter your product key. 
Review the Software License Agreement and click Continue. 
You must agree to Software License Agreement. Click Continue. 
Enter your product key and click Activate. 



  The Activation Wizard automatically contacts the Microsoft licensing
  servers through your Internet connection. When you activate the
  product by using the Internet, the product key is sent to Microsoft
  through an encrypted transfer. If you decide to activate the product
  through the Internet and you are not already connected, the wizard
  alerts you that there is no connection. Click either Activate by Phone
  or Activate later. 
  
  Note Do not lose the product key. Keep the packaging, or note the
  number. Keep the number information in a safe location.
  
  Your product key is a unique sequence of 25 letters and numbers
  divided into groups of 5. 
  
  If you purchased a box with a DVD: The product is located on the back
  of the Office for Mac DVD sleeve. 
  
  If you purchase through a web site: The product key is sent to you in
  email with the title Microsoft Office for Mac – Order Confirmation”