Answer:
Mrs. Smith is a postsecondary teacher, and Mr. Doe is a teaching assistant.
Step-by-step explanation:
Mrs. Smith gives the lectures, sets the due dates, and is an expert on the material of a "college-level course", therefore, she has to be a postsecondary teacher, as the teacher is responsible for giving the lectures, and has to be an expert on the material.
Mr. Doe helps grade papers, offers tutoring sessions for the students, and attends the lectures. From my experience and the phrase "helps grade papers" rather than just "grades the papers", we can conclude that Mr. Doe is the teaching assistant.