Answer:
Due to the nature of his friend's names, we can conclude that he does not literally mean that What, Why, When, How, Where, and Who are real people, but referencing the approach to an opening or introducing a question(s). Therefore, when he states that ,"She keeps ten million serving-men/ Who get no rest at all," his friend does not stop asking questions. It can be concluded that this friend is endlessly curious and wants to know the reason of action, or future actions, almost constantly.
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