The loss of original possession receipt should be made as a complaint before and obtain a non traceable certificate from police,  after which the flat owner should issue a public notice in a local newspaper,  wait for 15 days from the date of publication,  after that should submit an application to the society chairman requesting to issue a duplicate possession certificate. 

The owner should also enclose an affidavit indemnifying the society undertaking to resolve the legal complications in this regard that may arise in future, if any and also attach the copy of police complaint,  non traceable certificate from police,  newspaper copy and photocopy of the lost possession receipt held in his possession while submitting the request letter to the society. 

On receipt of the request letter you may place it before management committee members in your next meeting,  discuss about issuing the requested duplicate possession receipt as per the bylaws of the association. 

You should avoid taking any independent decision on such sensitive issues. 

ASk him to lodge FIR about loss of original receipt , issue public notice about loss of original receipt then only provide duplicate receipt after having resolution passed in MC 

He needs to obtain transfer of kabja from his seller. Society is not his seller. As a Secretary you can only endorse the  kabja certificate. He can approach his seller and request him to provide a duplicate certificate.

Dear client in order to provide the duplicate copy of any document you have to reach to the registrar and an application application for the duplicate copy.

You need to ask him to provide documents and then issue any receipt if required