Viewing other signals in OFDM

Hi. 

I am working with OFDM. I know that OFDM receiver in GNURadio needs a lot of parameters that are similar to the transmitter side in order to function. However, I want to attempt to view signals in OFDM receiver which are being sent using a non-OFDM transmitter. What I actually want to see is the frequency response of the signals on the subcarriers on the receiving side. What would be the right way to move forward with this?