So, in the Pre-Crisis, Earth 2 Superman and Lois Lane are married. Yet, from reading a few of the first Action Comics from '38, and just general knowledge of the Superman mythos, I know that Lois spent some time being unaware that Clark Kent was really Superman.
The question is, when does each Lois Lane discover (or have it revealed to her) that mild-manner reporter Clark Kent is really Superman? I don't mean "fake" reveals that she forgets at the end of the story arc through some sort of plot device, I mean the ones that stick until the overall continuity changes.
We basically have four Supermen*, so:
1. 1938 Superman/Earth 2 Superman?
2. Pre-Crisis Earth 1 Superman?**
3. Post-Crisis Superman?
4. New52 Superman?
I can already answer the last one:
Lois can be seen putting two and two together in Superman (2011-2016) #40, when a battered Clark walks directly past televisions showing footage of Superman sustaining the same injuries in a battle (Which, by the way, was a tremendous final sequence and cliff-hanger.). Then in Superman (2011-2016) #42, she rips open Clark's shirt to reveal the iconic Superman shirt (Yes, the New52 suit is iconic, get off my back already. I like body armor and high-collars. We all have our own tastes. ).
I guess people can discuss when Lois discovers the truth in other continuities- Elseworlds, TV series, movies, etc., but that's just if people want to go there. My question is about the four main historical in-continuity Supermen from the comics who were also Clark Kent (Well, really I am only asking about the first three- I answered #4 already, since I knew it and thought it should be included in case someone googles this thread trying to find out where they can see each Lois learning the truth).
* For the purposes of this thread, I am assuming Post-Crisis Superman is Rebirth Superman, or at least that Rebirth Superman is half of Post-Crisis Superman, and that when Post-Crisis Lois discovers who Superman really is, it's also Rebirth Lois doing the discovering in a Post-Crisis Pre-Flashpoint comic. If Superman Reborn reveals differently, we can add that to the list, assuming it isn't settled in that same story arc (i.e. "I'm really a different Superman entirely, and here's when Lois Lane discovered I was also Clark Kent in this great flashback!" or "I'm actually now both New52 and Rebirth Superman merged together, so Lois discovered my identity twice- once in Post-Crisis and once in New52!" or whatever).
** Did Pre-Crisis Earth 1 Superman's Lois ever discover that he and Clark Kent were one and the same? Obviously, the first Superman did, because they married, Post-Crisis did, because they also married, and I read the issues where New52 Superman did for myself. I sort of assume that Pre-Crisis Earth 1 Lois found out, but, to be honest, I'm not sure of that.