you
Explanation
The Joke
The comic shows a self-help book cover with the large title "YOU" and a generic image of a smiling blonde woman. The text reads: "Are sexually attractive and very smart, even though those are relative measures and this book isn't written to any particular human." The author is listed as "Zorkan Zorflex, PhD." The caption below reads: "The self-help books written by aliens were surprisingly popular."
The joke is that an alien, unfamiliar with human social norms around flattery and self-help, has written a self-help book that accidentally exposes the core trick of the entire genre. Human self-help books use the word "you" to make each reader feel personally addressed and special, but of course the book is mass-produced and not written to anyone in particular. The alien author naively states this contradiction outright -- you are attractive and smart, but these are relative measures and this is not personalized -- yet the book is still "surprisingly popular," suggesting humans will happily accept flattery even when explicitly told it is generic and meaningless.
The Humor
The humor lies in the satirical deconstruction of self-help books. By putting the honesty disclaimer right on the cover and still having the book be popular, the comic suggests that people do not actually care whether compliments are sincere or personalized -- they just want to hear nice things about themselves. The alien authorship is the perfect vehicle for this observation, since only a being unfamiliar with human psychology would be so bluntly transparent about the manipulative mechanics of the genre.