t's not uncommon that when mentoring somebody it is thought to be one way learning. The mentor shares their knowledge and mentee is expected to come up with questions. But true mentorship relationship can be as educating for both sides.
A good mentee asks a lot of questions. First of all it makes the job of the mentor easier when they can focus on the things their protégé is interested in and have identified they lack the knowledge or experience. Often they can even challenge the mentors knowledge which leads to a more valuable lesson than just reciting the knowledge.
By showing, and working together the mentor can not only provide (and learn) knowledge they didn't previously have, but they can also show the process how to get there. No knowledge can ever replace the ability to find or deduct new knowledge building on top of the existing one.
Mentoring others is also a great way to learn to know yourself. Reaching certain level of expertise you don't really think about how you do some things. They become so natural that it's hard to teach and share them. Such "intuition" is great when for example solving problems, but it also leads to a situation when those skills become harder to improve. You can make something you don't really understand better. You need to know how you do it to be able to improve it. And when you have to break it down to others you also open up a new learning potential to yourself.