Hi Assumptha,
You can use Modulation Toolkit to perform this demodulation. There is not a FSK example using DAQmx but there is one for FM demodulation to guide you to the process. To perform a FSK demodulation, you can use the shipped example "MT FSK Mod-Demod.vi" located under LabVIEW x.x\examples\Modulation\simulation examples\Programming
Good luck,
Gerardo O.
RF SW Engineering R&D
National Instruments