Hi Tristan,
I am not aware of any book devoted to Nock. However, Blackmore's book on British Military firearms discusses Nock in relation to his military contributions and inventions. In addition, most books that survey British gunmakers (e.g., Great British Gunmakers by Neal and Back) include examples of Nock's work. Perhaps W. W. Greener's book on firearms might also discuss Nock.
dave