How we can find out volumes of index Nifty?

Nifty is an index, it is not traded.

If you are looking to find volume, you can check volume and open interest of Nifty derivatives on Nseindia. At a time, there are three expiries traded of Nifty50 futures. So,you can check volumes of these future contracts.

 Nifty futures and options trading data at NSE Derivatives.