Naruto might feel a sense of responsibility. He would see it as his duty to help Boruto understand and control the Jougan. So, he could start to create special training regimens for Boruto. These regimens would be designed not only to strengthen Boruto's physical and ninja skills but also to help him master the unique powers that come with the Jougan. He would also teach Boruto about the importance of using such power for good and protecting the Hidden Leaf.
In fanfiction, if Naruto discovers Boruto's Jougan, it could change the power dynamics in the Hidden Leaf. Naruto would likely be both proud and worried. Proud because his son has such a unique and potentially powerful ability, but worried because it might attract unwanted attention. He could start to share his own experiences with dealing with unique powers more openly with Boruto. This might include stories about how he tamed the Nine - Tails' power. He would also probably consult Kakashi, his former teacher, to get some insights on how to guide Boruto in harnessing the Jougan's power safely and effectively.
Yes, there are. You can find Naruto has Jougan fanfictions on various fanfiction platforms like FanFiction.net and Archive of Our Own. Just search for 'Naruto has Jougan' on their search bars.
One of the most shocking revelations could be Naruto's early days as an outcast. Boruto, who has always known his father as a respected figure, would be surprised to learn that Naruto was once shunned by the village. Another could be the danger Naruto faced as a young ninja, like fighting against the Akatsuki. It's so different from Boruto's relatively more sheltered life in the beginning.
Archive of Our Own (AO3) is also a great place. It has a wide range of fan-created content, including Naruto fanfictions with the Jougan concept. The tagging system on AO3 makes it easy to search for specific stories.
In many fanfictions where Naruto discovers he has a sister, it often changes the entire dynamic of his story. It could give him a new sense of family and belonging that he lacked growing up. Maybe this sister was hidden away for some reason, like to protect her from Naruto's jinchuriki status bringing danger to her. This new relationship can also influence how Naruto approaches his ninja goals and his relationships with his friends.
If Boruto finds out about Naruto's past through fanfiction, it could initially create a sense of awe. Boruto might start to understand the hardships his father faced more deeply. He could become more empathetic towards Naruto. For example, learning about Naruto's lonely childhood might make Boruto appreciate his father's presence in his own life more. This discovery could also inspire Boruto to be more like his father in terms of determination and never giving up.