I am not a teacher.
Repartee is not a countable noun, so that's a big difference right there.
Of the other two, they are similar in as far as they are both used as replies.
A rejoinder is almost always witty and can be a reply to more or less anything, whereas a riposte is a reply to an insult or critical remark. It's a verbal counter-attack, and is also a physical one in fencing.
Student or Learner