“Do you know so-and-so?”
In its best form this question may be the entree to an introduction by the asker, sometimes it is fishing for an introduction for the asker, most often it is a conversational calibration tool (i.e. if you know so-and-so the conversation will go one way, if not it will go another).
For many years I have taken to answering this question the same way:
“Are you asking if I know them… or if they know me?”
For instance, at one time I was the personal banker for a very well known businessman in Tucson. I did work for him on a weekly basis, regularly interacted with his sister and other members of his family, received personal thank you cards from him when I helped associates of his, my parents attend a rather small Christmas party with him most years. I know this man fairly well… but I don’t think he could pick me out of a crowd.
This question of whether I know someone or whether they know me, is at the heart of a tension between the states of being recognizable vs being recognized. A recognizable person knows the right names and faces. A recognized person is known by the right names and faces.