I read somewhere that the better players actually take notes and have a small library of their notebooks. My solution was simpler, except for references like FCO and Opening Essentials, I've given up on books for the moment. Chess Mentor has everything I need in a much more accessible format. Well, that and videos. But then I'm not a "serious" player.
Forgetting what you studied

After reading a long chess book, alot of it just went in one ear, and out through the other. How do you avoid this?
That's a good question and like all good questions, it's one that needs to be asked over and over again.
My latest grappling with this sort of thing was to realise that there was no substitute for "being there" at the board in terms of trying to do better, rather than assuming I could just bring a bag of "knowledge" to the board. I have suffered quite a bit of frustration from working hard at the game to then overlook very simple stuff - and of course everyone does this to varying degrees !
What we study away from games is important and it's often said that studying our own games is one of the most important things to do.
We can't always assume (chess) books are well written. Good writers make subjects accessible and in doing so make the reader feel "smart", whereas bad writers IMO, affirm their own egos and confound their intended readers.

You aren't necessarily supposed to remember all the concrete stuff but rather the general principles behind it all. We read a note in Fine's Basic Chess Endings (or nowadays Dvoretsky's Endgame Manual since it displaced BCE as the definitive endgame book) going over a principle then look at concrete variations confirming it.
The foremost aspect to improve, aside from endgame technique, should be judgment, for if one misevaluates a position 9 moves (18 ply) ahead then they have a certain ignorance they need addressing. Maybe they overestimated their static advantages and greatly underestimated the opponent's dynamic advantages? What if one of the 18 half moves was a mistake assumed to be optimal, overlooking a critical refutation (such as an in between move that busts the line somewhere whereas an immediate recapture would be a normal position)? There is so much to correct about our thinking in chess.
OP I think you've hit on a major question in chess.
It's very easy to waste your time. There's suboptimal use and there's in one ear out the other - forgetting everything like you've read it.... which is a pretty brutal prospect if you were doing hard work.

After reading a long chess book, alot of it just went in one ear, and out through the other. How do you avoid this?
#leftear

A good thing to do is pretend you're getting examed on the material. Write down questions pertaining to the topic discussed. Include specific positions with side to move and ask a relevant question. For Soltis' Pawn Power Chess one can write a question: "What are the advantages and disadvantages of the Boleslavsky Wall? How to play against it as white and with it as black? Is a Marco Hop always a good idea? Why or why not?" or in My System, "Is a pawn center always an advantage? Why or why not?" or Masters of the Chessboard, "What are the drawbacks of 1.e4 and 1...e5 against 1.e4 respectively? What is usually better in an attack down the h-file queen in front of rook or rook in front of queen? Why?" Stuff like that. Then you check your answers against what the author himself wrote and grade accordingly. Then take the quiz again the next day, the concepts should be reinforced.
If you get an A in your chess studies you should see a rapid improvement.

Don't mistake 'forgetting' with 'not being able to apply'.
The problem may not be you, but the fact that what you study my not, for the most part, be immediately applicable to your games.
Here is a blog I wrote that may help you along:
http://www.chess.com/blog/kleelof/the-nature-of-imporvement

Everyone forgets what they read. Retention improves with application, repetitive practice, rereading. As with any subject, you read faster and remember more when you are reading the tenth book on the topic than when you are reading the first.
Earplugs help, too. They reduce distractions. However, they can cause discomfort.

Earplugs help, too.
If you are wearing earplugs, how is it supposed to go in one ear in the first place? I think you had it right earlier with the 1 earplug idea.

that may be mother's theory... learn with facepalms..... auuuu
Sounds like our mothers went to the same school of discipline.
After reading a long chess book, alot of it just went in one ear, and out through the other. How do you avoid this?