When did this substitution come into effect?
The substitution came into effect on 16th September, 2016. This is stated in the context provided where it says "Subs. by the Constitution (One Hundred and First Amendment) Act, 2016, s. 13(ii), for "sale or purchase of goods takes place" (w.e.f. 16-9-2016)." The term "Subs." stands for substitution, "by the Constitution (One Hundred and First Amendment) Act, 2016" indicates the amending act in question, and "s. 13(ii)" refers to section 13, clause 2 of this act. The phrase "w.e.f." stands for "with effect from", indicating when the substitution came into effect, which is on the date mentioned in brackets, i.e., 16th September, 2016.