The easiest test of your CAN network is enumeration. If you can enumerate the Jaguars, then your cabling works. (You can test this with the cRIO or with BDC-comm. Enumeration is in the functions pallette under "WPI Robotics Library">Communications>CAN. The BDC-comm enumerates automatically when you open it up - the Jaguars you can select from the drop-down menu are the ones it enumerated.)
If enumeration works on the cRIO, then the issue is probably the Jaguar firmware; the Jaguar firmware must be updated (using the BDC-COMM) for using CAN in FRC.
If enumeration works on the BDC-COMM, but not on your cRIO, then there's probably an issue with your CAN plugin, or your code.
Now, it's entirely possible that your CAN network and code is working correctly, and you are simply not enabled or do not have DS communication. Make sure you have a "StartCommunication" on your block diagram. (This can be found in the DriverStation subpallette of the "WPI Robotics Library" functions.)
EDIT:
You asked for an example. I have a repository with a default project modified to CAN here:
https://github.com/kamocat/ThunderTech_3213/tree/CAN
If you'd like something specific, you can upload your code or state exactly what you're testing.