As far as I know, it isn't possible to read the state of a digital trigger from the digital trigger pin in a data acquisition board. However, I might be wrong!
I would suggest you to wire the digital trigger signal to both the digital trigger pin and TO ONE DIGITAL I/O LINE of the data acquistion board. You can read the state of a digital i/o line with the "Read from Digital Line.VI" in LV, or with the NIDAQ function call "DIG_In_Line (deviceNumber, port, line, state)". First, LV return a boolean regarding the state of the line which you can use to change the case of your case structure, and CVI returns a 16-bit integer, which you can manipulate to do the same as in LV.
Hope this information is helpful.
Aguila