What have you done today? - Yes, fine. A summary, an instant in time when one adds everything up. What have you been doing today? - Yes, fine. What has occupied time? about where has the time gone. . I have been typing, answering for a minute or so, now the questions has an answer.

I'll say it here as well! Yes, you may say both. They are both in the present perfect tense. The 1st is active voice. The 2nd is passive voice. They will likely produce the same answers in the simple past tense (e.g. I went to the store today and then I...).

Yes, you can say both, and they mean almost exactly the same thing. "What have you done today?" tends to refer to completed actions: "When I saw my friend this evening, I asked her: "What have you done today, and how many of those same things will you have to do again tomorrow?" "What have you been doing today?" tends to refer to actions that are still ongoing: When I met my friend for lunch, I asked her: "What have you been doing today, and do you think you will get it all finished by the end of the day?" However, if you exchanged "done" with "been doing" in my example sentences above, both would still make perfect sense; and be something that native English speakers say all the time.

Yes, you may say both. They are both in the present perfect tense. The 1st is active voice. The 2nd is passive voice. They will likely produce the same answers in the simple past tense (e.g. I went to the store today and then I...).