Hi! Gaganpreet
Sorry i was busy in my research work and hardly get a time now a days to do reply on forum more frequently.here if you want to see the fwm signal ,it can be easily seen from OSA.However if you want to plot then you need to select one parameter for example input power on x axis and fwm power on y axis.In this way you can plot fwm signal power vs input power and even add signal power vs input power.Is this your query ,because i dont get how you asked to plot fwm vs freq.
In case you have seen this type of plot then attach screen shot and this will be more clear to me.