Question

What is “i have never met a man so ignorant that i could not learn something from him” mean

Answer 1

It means that the ignorant people (idiotic people) hat she has met all taught her a lesson but this man that she met was so ignorant that she didn’t learn anything about/from him

Answer 2

It means that the person speaking has never met a man that is so idiotic or stupid.

The speaker says that "i could not learn something from him" so he could give an example of how ignorant the man the speaker is talking about is.