What is the best location of waffer type check valve in pump discharge and why.

Pradeep,
I'm not sure what you're asking. Beginning at the pump's discharge flange, and assuming a typical centrifugal pump & at least one spare pump piped in parallel, I'd install a pressure gauge, then any desired flow measurement relating to pump's minimum flowrate, then any needed minimum flow line for that pump, then the check (non-return) valve, and then an isolation valve. Because you state that the check valve is to be a waffer type, you may need to install an extra pair of flanges and a short spool peice between the check & isolation valves if the construction of the latter might interfere with a full opening of the check valve. If you need additional information, please supply us with additional info regarding your concerns.