Author of many of the immensely popular Künstler-Monographien series of Velhagen & Klasing publisher. Knackfuß entered the Dusseldorf Academy in 1869 to study (studio) art under E. von Bendemann and E. von Gebhardt. He joined the Hussar regiment for the Franco-Prussian war making drawings of the conflict. He received a travel prize to study in Rome, 1875-1878. Upon his return he married the daughter of the sculptor H. M. Imhof. In 1880 he was called to the Dusseldorf academy to learn art anatomy. He travelled to Greece, Egypt and Asia Minor to sharpen his skills as a history painter.