As I write in this comment detailing my strategy for using Anki to learn material from textbooks, Peter Gray's Psychology is particularly suited for ankification. Each page from that textbook comes with 1-3 marginal "focus questions" intended to guide the student in the process of learning the material. One can simply write these questions on the front side of the card, and on the back side write a brief summary of the paragraph(s) to which the questions refer. For an example of how a card written in this way would look like, follow the link above.