One way to skim a (non-fiction) book effectively is to read the opening chapter (or intro) then flip through the book reading each chapter’s opening and closing paragraphs, the subhead, and the side bars. I even read every 20th or 30th page.
Then, quickly, write down the main thought in one sentence, followed by the three supporting thoughts that seemed most important. This seals the book in your memory.
I use a digital note file I can back up so I don’t lose them.
You shouldn’t skim fiction or poems, but you can skim first and read a second time. If you put it down because it doesn’t connect, return in a year or two. You may find it more engaging. Vonnegut just didn’t connect with me in high school. I consider him a major influence now.