There are quite a few things. For one, he could teach past Naruto about the deeper secrets of the Uzumaki clan. Since Future Naruto has explored more about his heritage. He could also give tips on handling the Kyuubi's chakra more smoothly. Maybe some new jutsu combinations that he discovered over the years. And not to forget, how to better read an opponent's moves during a fight, which is a skill he would have refined over time.
In fanfiction, Hinata could teach Naruto about the Hyuga clan's gentle fist style. Since Naruto mainly focuses on his own powerful and straightforward combat techniques, Hinata's more refined and precise style could be a new area of learning for him.
In a more creative fanfic, an ancient ninja who was the originator of the Chidori technique could appear. This ninja could be brought back to life through some sort of magic or jutsu. He sees Naruto's pure heart and decides to pass on the Chidori knowledge to him, believing Naruto will use it for good.
Maybe an ancient sage in Naruto's own world who has long - been in seclusion. This sage has knowledge of different power systems beyond just chakra. He notices Naruto's pure heart and strong will and decides to pass on his knowledge of haki to Naruto, believing that Naruto can use it for the greater good of the ninja world.
It could be a wandering sage. These sages are often full of strange and powerful knowledge. They might see potential in Naruto and decide to teach him hypnosis as a way to expand his combat skills.
First, Naruto would need to understand the rabbit's semblance fully. If it's a strength - based semblance, Naruto could teach the rabbit by demonstrating his own physical training techniques. He'd show the rabbit how to build up power gradually, starting with small jumps and then progressing to more powerful leaps. He'd also encourage the rabbit by sharing his own stories of how he overcame difficulties in training. And he'd use positive reinforcement, like giving the rabbit its favorite food when it makes progress in using its semblance.
Well, a sentient library might use its knowledge of all the Naruto lore. It could teach Naruto fanfiction by categorizing different types of fanfictions based on their style, for example, adventure - focused or character - centric. It could then guide the writer by showing examples of successful fanfictions in each category and what makes them good.
In a fanfiction, Sakura could be the one to teach Naruto to pole dance. She has become quite skilled in various forms of combat and physical training over the years. She could introduce pole dancing to Naruto as a form of alternative training that focuses on different muscle groups and balance. And since they are friends, she would be patient with him during the learning process.
Naruto could teach about the power of friendship and loyalty. In his own story, his relationships with his friends were crucial. He might pass on these values to the RWBY characters, making them understand that they are stronger together. He could also teach them some basic ninja tactics like how to set up traps or how to gather intelligence.
Naruto might be a great professor for a class on the study of magical creatures. His curiosity and ability to befriend all kinds of beings in his own world could translate well. He could teach students how to approach magical creatures with respect and understanding, just as he did with the giant toads and other beasts in his ninja journey.