Perhaps Gordon gets a tip-off from an unexpected source or manages to access hidden information that leads him to discover Batman's identity. It could also be a combination of multiple small clues that finally add up for him.
Well, it might happen when Gordon stumbles upon some crucial evidence or has a moment of realization based on his long-term observations of Batman's actions and behavior.
Well, Gordon's reaction could be complex. On one hand, he might feel honored that Batman has chosen to disclose his identity to him. On the other hand, he could also be worried about the implications. Knowing Batman's identity means he has a greater responsibility to protect that secret. He might start to think about how this new knowledge will affect their working relationship and the safety of Gotham. For example, if the wrong people find out that he knows Batman's identity, it could put him and his family in danger.
Well, it could lead to all sorts of dramatic and unexpected turns. Maybe Commissioner Gordon has a hard time coming to terms with it or uses the knowledge to protect Batman in a new way.
Fanfiction explores their relationship in various ways. Some stories focus on the mentorship aspect, like how Batman trained Barbara to be Batgirl. For example, in 'The Mentor and the Protégé', it shows the early days of their relationship, with Batman teaching Barbara combat skills and detective work.
Jim Gordon might initially be in disbelief. But then, considering all the times Batman has helped him and the city, he could come to accept it. He may also start to see Bruce Wayne in a whole new light, realizing that his playboy persona was just a cover for his nocturnal activities as Batman. He might even become more protective of Bruce's secret identity, as he knows how important Batman is for Gotham.
You can try fanfiction websites like Archive of Our Own (AO3). It has a large collection of various fanfictions, including those related to Batman and Gordon. Just search for 'batman gordon slash' in the search bar and you'll likely find a good number of stories.
Batman is often portrayed as the brooding, dark vigilante. He's highly intelligent, with a strong sense of justice. He's dedicated to cleaning up Gotham but is also a loner at heart. Jim Gordon, on the other hand, is the honest cop. He's morally upright and willing to work with Batman despite the fact that Batman operates outside the law. He's a family man and is seen as the bridge between the law - abiding citizens and Batman.
In some fanfictions, it might be through a sudden reveal or a series of clues that lead him to the truth.
One great 'Batman Barbara Gordon Fanfiction' is 'Oracle Rising'. It really delves into Barbara's transformation into Oracle. It shows her strength and intelligence in a way that's both engaging and true to her character.
One more theme is the exploration of her dual identity. As Barbara Gordon, she is a librarian or a normal citizen, but as Batgirl/Oracle, she is a crime - fighter. Fanfictions play with this duality, showing how she balances her two lives. Sometimes she has to keep secrets from her friends and family, and this creates interesting plot twists and character dynamics.
It could be through a magical reveal or a series of mysterious events that lead her to the truth.