Hi Intern,
PFI lines can be used for input or output, yout test will depend on what do you want to proove. To test them for output you can export the Data Active event using the VI that ryan describes (there are restriction on where you can export clocks) and run the example "Dynamic Generation with DAta Active Event"; you should see a pulse on the PFI line when data is being generated.
For input, you can configure a trigger and provide a pulse externally, if your acquisition completes with no errors after you provide the trigger, then the PFI is working fine.
If you can connect some PFI lines together you can use the "Dynamic Generation and Acquisition Source Synchronous" example to export data active to a PFI and use it as a trigger ina nother PFI line, the example has documentation on what is going on.
I hope this helps,
JC