I do BTST many times a year and trading is my only income. Then should I show it as 'Speculative' or 'Non-Speculative' business income?

It will be considered as speculative since you are not taking the delivery of the shares here.

I have read the ‘Taxations Module’ of Varsity and have understood many aspects of it but I still have some confusion which I have asked above?

Yes, Intraday equity is considered as Speculative.