My experience, for what it’s worth, is that book notes I’ve taken for reference purposes rarely get discovered again in my workflow. So a simple idea I’ve adopted in my note-taking, that builds on collecting quotes and references, is to make “Notes to self” that summarise my own thinking or connections as I’m reading and thinking about what I’m reading. I literally write “Note to self: …” followed by my thoughts, so that I can find these notes easily and differentiate them from quotes, references etc.
This practice can be followed anywhere you take notes: in other apps, on paper, in books/readers… You can then conduct searches for “notes to self” and export those notes, and turn them into Obsidian atomic notes, and start connecting notes. Those atomic notes provide the breadcrumbs back to your original book notes and references, and increase the chance of re-discovering stuff you’ve squirrelled away.
I’ve shared some more detailed thoughts on another thread here: What has your PKM actually help you achieve? - #10 by NeuroJitsu