The checked baggage allowance should be 20kg for Y, 30kg for J and 40kg for F. However, SQ honours ticketing mistakes. Here is my personal experience.

I had an SQ CDG-SIN J reward ticket issued by Air Canada's Aeroplan. I should only be allowed 30kg check in, but AC made the mistake of printing 2pcs on the ticket for checked baggage allowance. I called SQ in Canada and Singapore to verify, and they both said that SQ has to honour what's printed on the ticket even if it's not what the passenger is really entitled to. So, see what's printed on your ticket / e-ticket and proceed accordingly.