But the thing is that I don’t have any idea about purchase as earlier it was mentioned by my father who passed away few years back.
Is there any reference date from which I can calculate LTCG ?
Also Is it necessary to show this detail in ITR. ?
Do not worry too much about this, if the shares you sold are listed on which you paid STT then simply mention the purchase price as Nil. Anywhich ways the tax on this income is zero. And yes you need to show this income in ITR.