I wonder whether a public speaking class could be taught over the internet. I know nothing about how this skill is taught, but I would guess that it is much like any other performance art. First you watch people doing it well, then a group leader shows you how to analyze good performance. Next you each try doing it yourself, and the leader guides the members of the group in critiquing each other. Rinse and repeat, for each specific skill or genre in this art form.