He has a page or two in most of his books about the
caged idea, I think. I have his 'Fretboard Roadmaps - Blues ' and that has two pages about CAGED. To be honest I think you'd do as well to Google for CAGED if
all you want is information about the CAGED system.
(Not to be taken as a criticism of Mr. Sokolow's otherwise excellent books BTW, just a comment on the reference to CAGED theory the copy I have contains)