How to see Signal frequency and Sampling frequency on the frequency spectrum
If you sample a 100Hz signal at 3kHz, then here's what you will see:


Time domain: Think of this as a digital oscilloscope view.  You will have a series of numbers that represent the voltage.  These numbers are spaced at 1/3000 second along the time axis.  Basically, a bunch of dots on an xy coordinate system.  X is time, and all of your dots are 1/3000 of a second long.  Y is voltage, and your dots are at the height indicated by the voltage.
Frequency domain:  You take your digitized data, and apply a fourier transformation to it.  You now have a bunch of dots which represent the intensity of each frequency in the signal.  The frequencies range from 0 to 1500Hz. Refer to the Nyquist/Shannon theorem for the reasoning.  In your (idealized case) you will see a single peak representing 100Hz.


The sampling rate is not part of the spectrum.  You'll never see it.

The sampling rate is also not part of the digitized data - you would never see it in an oscilloscope view of your data.



Really, you need to look up sampling theory.  The wikipedia link is a starting point.  If you understand what is going on, then you would never wonder how to seperate signal and sampling rate - you would know that they are already seperate.