An account written by Plato. It includes the moment when Socrates questions Protagoras on the teachability of rhetoric, or rhetoric as an art that can be taught (rhetorike).
Socrates, however, turns the dialogue into a discussion of “the art of citizenship,” which in Athens, was, in some ways, inextricably bound to the art of rhetoric. (Or at least scholars like Poulakos would argue the Sophists, of all rhetoricians, made most evident to the Athenians, pre-Plato, pre-Aristotle.)
The question that instigates the “Great Speech” by Protagoras is asked by Socrates: “So if you can clarify for us how virtue is teachable, please don’t begrudge us your explanation” (p. 48)
Hippocrates wishes to become a student of Protagoras, but Socrates uses this moment to being a line of questioning, where Protagoras must defend his claims that he can teach the art of rhetoric, or art of good citizenship.