how does your character learn stuff?

In a story – especially one with mystery elements – how does a character discover information? She can't find it all from one source, be it a person, a book, a newspaper clipping. There has to be a variety of sources involved. It makes me think of Harry Potter and J.K. Rowling's invention of the pensieve, and I simultaneously curse and bless her again for her genius. With a pensieve, Harry could drop himself directly into someone else's memory and watch it as if it were taking place in the...