Well, Naruto would probably become extremely powerful. Kami has great power and knowledge. With Kami's training, Naruto might learn some really unique and powerful jutsus. His understanding of chakra could reach a whole new level.
Perhaps it could be a female version of an existing kami from Naruto lore. For instance, a female counterpart of the Sage of Six Paths. She would have vast knowledge and power, and her training of Naruto would be a way to pass on that ancient wisdom and strength.
He might gain enhanced chakra control. Since Kami is a powerful entity, Naruto could learn to manipulate his chakra in ways he hadn't before, like creating more complex jutsus with less effort.
In the 'naruto trained by fem kami fanfiction', perhaps the fem kami sees Naruto's potential and decides to train him secretly. She might introduce him to new realms of chakra control and spiritual awareness. This training could involve Naruto having to face otherworldly challenges that are far beyond what he's used to in the Hidden Leaf Village. It could also lead to Naruto having a different perspective on the ninja world as a whole, since he's being trained by a being from a different plane of existence.
He becomes more patient. Kami's training likely involves a lot of self - reflection and inner - peace - seeking, which forces Naruto to slow down and think more before acting. This newfound patience helps him in both combat and his relationships with others.
He might gain enhanced spiritual powers. Kami could teach Naruto to better sense and interact with spiritual energy, which could give him an edge in battles against opponents with spiritual - based attacks.
In some fanfics, Naruto might be made to hate Kami due to a misinterpretation of Kami's role. Maybe the author wants to create a new narrative where Naruto rebels against the traditional concept of Kami in the Naruto universe.
Another unique feature is the exploration of a different kind of relationship between Naruto and the Kami. Instead of just being a distant, unknowable force, the Kami in these fanfics can be a mentor, a friend, or even an adversary to Naruto. This creates new and exciting storylines that expand on the original Naruto concept.
It's hard to say for sure. There are so many Naruto fanfics out there, and popularity can vary greatly. Some fans might be drawn to the unique concept of a 'godlike' Naruto being married to Kami, while others might prefer more traditional or canon - based storylines.