You can check out the whole guide, but "emotional hookpoint" is a specific analogy to the normal pickup concept of "hookpoint." The hookpoint is the time early in the interaction where the woman realizes that she is attracted to the PUA and/or wants him to stick around in the interaction (i.e. the PUA "hooked" her).

The author of the playette guide is using this concept to make an analogous observation for female pickup. By "emotional hookpoint," I think she means the point where the guy starts becoming emotionally invested, and/or starts getting a "crush," and/or starts wanting a relationship with the woman. (Of course, those aren't all quite the same thing, so I don't know exactly which she is referring to, but they often go together.)

I think this analogy is brilliant and quite accurate; I've felt myself hit the "emotional hookpoint" when I find myself thinking, "shit, I'm getting a crush on this girl."