So in the latest Justice League, Batman takes control of the Mobius Chair after Diana takes it away from Metron. He asks it who killed his parents to see if its all-knowledgable as its supposed to be. It gives the correct answer. Batman then asks his next question: What is the Joker's true name? The Chair tells him. And its something that shocks Batman as he answers "No, it can't be...". So yeah, I don't know if this will ever be utilized in his main books, but he knows who the Joker is now. And its clearly an identity that is familiar to Bruce Wayne on some level. Enough for him to be shocked at the answer.