What was Wonder Woman doing during the events of Man of Steel?
We don't know exactly but she just walked away from humanity, as she explained to Bruce in Batman v Superman: Dawn of Justice:
BRUCE WAYNE: They will. And they'll fight. We have to stand together.
DIANA PRINCE: A hundred years ago I walked away from mankind. From the century of horrors. Man made a world where standing together is impossible.
BRUCE WAYNE: Man is still good. We fight. We kill. We betray one another. But we can rebuild. We can do better. We will. We have to. - source
But we later see in prequel Wonder Woman that she did participate in World War 1 and the sequel Wonder Woman 1984 is set in Cold War time, maybe in this film or later films we will get to know the exact reasons why she skipped WW2 or Zod attack but for now we have to take her words from BvS.