When you’re listening to audiobooks, I don’t think it’s appropriate just to listen. To fully comprehend, you have to keep an outline of the book on a page in front of you. This isn’t so you can reference it in the future, it’s to make you pay attention. When you have to summarize each section, you have to listen closely. If you didn’t fully understand it, you have to go back.
You cannot fake your way through a summary as you did in school. (You’re also not doing it for a grade anymore, so you can focus on real learning rather than proving you read the book.) As you keep the outline, keep it simple. Don’t stress yourself out by writing each and every idea, but don’t put the pen down for too long. Once the pen goes down, your attention seems to wander. If you want to continue to listen to audiobooks, you’ll train yourself to really listen, not just hear.