SQ agents can view total number of unsold seats, but it's commercially sensitive information and agents are not normally allowed to give precise numbers to passengers. Of course, some do anyway, but you shouldn't count on all agents willing to bend the rules that way.

Why do you need to know the precise figure? Are you planning to change the flight if there's only 26 spare seats, as opposed to 60 spare seats? What I'm trying to say is, is it not sufficient to know that a flight "has a fair number of empty seats" as opposed to the flight "has 60 unsold seats"?