Interesting question, and the way I’d want to tackle it is by defining what it is that unpaid work means. See also Could writing on Quora be considered voluntary work?
Work is undertaking an obligation to do tasks, that in themselves benefit another more than yourself. The compensation for work may take the form of payment, or barter, or incurring an obligation, or not being beaten to death as a slave; but the work itself is not meant to be its own reward. That tends to rule most of us out.
The closest to an acknowledgement of Quora contributions as work is by Stephanie Vardavas, in her answer. Community moderation tasks are less for fun, and more out of a sense of obligation to the community. But still, it’s community work; Quora Inc may benefit out of that work, but I trust Stephanie isn’t motivated to collapse trolls out of admiration for D’Angelo’s blue eyes. So it’s not the same as Work For Quora; and indeed, the community work Stephanie does benefits Stephanie as a member of the community.
I think it’ll be hard to find anyone considering Quora contributions as work to benefit another; possibly academics counting this as part of their Community Outreach?