I read via epubs. I highlight useful passages. On passages that are vague but meaningful I highlight in a different colour and add a note over it that appears when the highlight is clicked.

I don't note near as much as I highlight however. Just note whatever requires addition thought beyond the material presented.

>>8234645
What app do you use

>>8234634
I jot down general summaries in a separate notebook, while more liberally bracketing/underlining passages in the book itself. After finishing the book I'll re-read my separate summary, then flip back through the text looking at only the sections I marked. If they're relevant on the broader scale of the whole work, I make notes of them; if not I just pass by them, or save them IF they're at least curious/interesting.

>>8234650
Depends. Some books are on Google play - a great app, built in one-touch dictionary as well and carries across all devives your account is on.

For books I torrent, I use Universal Book reader (Android) and for IOS I use Ibooks. Make sure your files are .Epubs as you can't highlight or annotate on a .Pdf, just bookmark.

>>8234634
marginalia and a stupendous memory, generally. i am also frequently struck by some brilliant lines of commentary; this i record on an index card, in the corner of which i mark the page of the passage which inspired it. then, i tuck it into the spine and continue along. i have whole papers stored in the books which will be their subject matter.