Is it possible to visualize a 2.4 GHz digital signal without an oscilloscope?
According to the data sheet, the N1996a spectrum analyser has a 'zero span' mode, where you can use it as a fixed tuned receiver, and the trace sweeps in time rather than frequency, just like an oscilloscope. See page 101 of the manual N1996-90028.pdf

Set the resolution bandwidth to be wide enough to follow your signal.

If you tune it to the centre of your RF signal, then you demodulate the AM.

If you off-tune it, so that you are 20dB or 30dB down the side of the filter, then you can crudely demodulate FM. As the frequency varies, the response moves up and down the slope of the filter. 

With both AM and FM demodulation possibilities, you ought to be able to get some response, whatever the original signal's modulation.

I notice the R4131D has zero span, as well as video and IF outputs, so the analyser can be used as a fixed tuned receiver, and you can display the IF or video on an oscilloscope.