You cannot acquire the trigger signal directly from FPI0. You need to wire it to its own analog input to be able to digitize and visuzlize it.
In general, trigger signals have much more bandwidth (quick transition) than the signal that is actually desired to be acquired. It means that digitizing a trigger signal would often require a much faster Analog-to-digital converter than what is available. So, if you wire the trigger signal to an Analog input, unless the board is fast enough, you will likely get very little information.
Marc Dubois