Complex sentence: René Guénon wrote a detailed critique of Theosophy entitled "Theosophism: history of a pseudo-religion" (1921), in which he claimed that Blavatsky had acquired all her knowledge from reading books, and not from any supernatural masters.
Split into simpler sentences: René Guénon wrote a detailed critique of Theosophy titled "Theosophism: history of a pseudo-religion" (1921). In the book Guenon claimed that Blavatsky had acquired all her knowledge naturally from other books not from any supernatural masters.