Translation:How do you say good afternoon in German?
It's like the passive voice, "how does one say," or "how is it said." It has the same meaning of "how do you say" or "how do I say" in English, because those questions aren't exactly asking how "you" or "I" personally would say that, but how "it is said," in general, impersonally. Romance languages are sometimes more vague and flexible like that. Out of context, it can really mean any of those, but most literally I think it's along the lines of "how does one say..."