It is independently available as a paperback, but also the "pre-fascicle" (draft version) is available for download: http://www-cs-faculty.stanford.edu/~knuth/fasc6a.ps.gz or click on 6A at http://www.cs.utsa.edu/~wagner/knuth/ specifically: http://www.cs.utsa.edu/~wagner/knuth/fasc6a2015.09.23.pdf

His programs (SAT solvers) are also available on his site at https://cs.stanford.edu/~knuth/programs.html (They are in CWEB and you'll have to use cweave and ctangle to read and run those programs respectively; if you just want to read I've typeset them here: https://github.com/shreevatsa/knuth-literate-programs/tree/1...)

Knuth has also given a couple of talks about satisfiability around the time he wrote the book:

- https://www.pathlms.com/siam/courses/3028/sections/4140/vide... (July 2016, at SIAM Annual Meeting)

- https://www.youtube.com/watch?v=g4lhrVPDUG0 (December 2016, at Brown University)

Look at https://cs.stanford.edu/~knuth/news16.html#lectures for slides and handouts from these talks.