Depends on the book.
Many of them I don't finish. Some because starting the book meant just sort of browsing around and they stayed that way. Some that I started and read sequentially until I didn't and then maybe I browse in it or maybe I don't. Some because the book's content gets beyond my knowledge or interests or both.
Of the technical books I finish, it depends on the book. Depth of content, my level of relevant knowledge and the length of the book all play a role.
The pace at which I tend to read technical books when I am committed to reading them (but perhaps not finishing them) tends to be about twenty or so pages a night most nights while I am in that mode. That might mean ten pages a night for a deeply technical book (or thirty if it is so deep I am skimming it). It rarely involves doing exercises though sometimes it involves reading them.
For full clarity, I don't really worry about what I miss or not getting 'everything' out of everything I read. A lot of books are over my head. A lot extend beyond my interests. Also, I'm not in a hurry because the more other things I learn, the more I will tend to get out of any particular book.