Books are an excellent source of information.
Generally speaking, though, telling someone you read a fact in a book (even non-fiction) isn't sufficient to make them instantly trust that the fact must be true. Especially in today's market where anyone can publish a book themselves. Even if it's a respectable source, unless the person you are talking to recognizes and is familiar with the author, it's not going to be sufficient to lend credence to your argument.
If you were talking with someone and they mentioned the blue sky and you came back with "The sky isn't blue -- I read it in a book" and leave it at that, you are not contributing to the conversation, regardless of the method you chose from your example to deliver the statement.
Your comment will be interpreted differently depending on who you are talking with. Some may think that you're referring to sunset, when the sky changes color. Many may recall back to childhood science classes, being told that a green object looks green because it absorbs the other colors and the joke that it's actually all the colors you don't see. Perhaps they will turn the idea that the actual molecules themselves in the sky aren't colored, and we aren't seeing them. Others may interpret it as a dig against pollution, and how the sky is getting discolored because of smoke.
Regardless of whether it's a fact or an opinion, a statement isn't contributing to the conversation unless the other party understands why it is being made.
It's the same with a book.
Non-Fiction books (at least, good, compelling ones that you will be quoting) do not simply list facts. They describe the science or history that led to the fact and give a full description of what it means and why it is important.
If a book tells you "The sky isn't blue" then it doesn't matter if it's fiction or nonfiction, you aren't going to accept that argument just because it's written down. A decent article, however, will go on to say "The sky is predominately a combination of blue and violet wavelengths -- it looks blue to humans because the neural signal from our eyes processes the combination of blue plus violet light the same way it would handle blue plus white light." It could go on to talk about how if humans evolved an extra range of cones, they would see the sky differently than when they're looking at what we perceive to be the same color blue.
If you are going to use "Book Learning" in conversation, you should keep the same thing in mind. Telling me a fact is not useful. It does not contribute to the conversation, and it is likely not interesting enough for me to remember. So don't just tell me that Multitasking isn't possible -- I eat while watching TV, I listen to music while driving. Explain to me the rationale that led you to believe the book when it told you Multitasking isn't possible.
tldr; "Book Knowledge" isn't any different from any other knowledge you might have. Examples 1, 2, and 3 are just hooks to get the other party interested in a topic, or to find out if they're already familiar with what you're about to talk about.
Which one you choose isn't nearly as important as what you say afterwards.
1) "I read a book on productivity and it said multitasking isn't possible. Apparently, the research shows .... Frankly, I have a hard time believing it, because..."
2) "Multitasking isn't possible. People think they can multitask because... "
3) "I've heard that multitasking isn't possible. The claim was that..."