From The Refusal of Work, by David Frayne, pg 199:
What do you do? After ‘What is your name?’ and possibly ‘Where are you from?’ this is one of the first questions that strangers usually pose to one another, with convention dictating that this question is almost always an enquiry into our employment situation. ‘What do you do?’ means ‘What job do you perform?’ If we are being generous, we might say that the posing of this question is innocent enough. It represents a social custom, or an attempt to elicit information that might bring relief to the interaction by providing it with some context, pushing the conversation towards some common ground. If we are being more critical, we might view this question of ‘What do you do?’ as a naked attempt to measure the status of the other. ‘What do you do?’ means ‘Summarise in a sentence what you contribute to this world, and I will judge you on the basis of your response.’ Or ‘Are you a person worth knowing?’