Run this script from the command line on an administrators workstation. The script will read the URL to your JSS from your standard plist file. It will assume your login name to the JSS is the same as your login name for OS X. And finally, you will be prompted for your JSS password.
You can edit the script and un-comment the following variables and edit them with your specific information to override the username and to avoid password prompting.
This script will use the REST API to enumerate all computers in the JSS and list those that do NOT have a Last Check-in time. It is designed to run from an administrator's workstation and the results can easily be piped to a text file. Depending on the size of your JSS the script may take several minutes to complete. Please be patient. Use as your own risk.