Hi Kamal,
Assuming as your very familiar with BW extraction.
in such case just find the primary info objects which has been used in your target(dso/cube).
To know the info object names you can look at table - RSOSFIELDMAP thru your data source name.
You ned to activate your data source at crm side and replicate int bw(7.x). later activate it.
After that you can check above table, will shows related info objects.
Later with help of info objects you can look for master data sources at CRM RSA5 under crm application component.
hope it helps,
Thanks
Raman