The account identifier allows support to recognize/identify the account and information related to any registration specifics. It will be needed for any correspondence about your purchase or registration
and can be located on the "About" screen on any of the applications - Neal's Cars, Neal's Weather, etc. The tablet apps and the phone apps use the question mark graphic ("?") to navigate to the "About" form. Any expired application will show it on the "Expired" page also. Most of the accounts have clickable links or are able to copy the account to the clipboard. If you click the clickable links you will navigate to the web site where information about the account will be displayed.
Here are images of where to locate it in the Cars application on a tablet: