I read this post so I understood why we need an article in the sentence
What do you do for a living?
My question is why we use
a living not
the living, since we are asking certain somebody, shouldn't we use
the instead of
There are many possible 'livings' - i.e., professions, vocations, jobs. So I have 'a living', not 'the living'.
living (MW, noun definition 2)
means of subsistence : livelihood