How would I cite the words of a guest speaker in APA?
I would advise you to consult with your professor to determine the type of source the guest speaker is, an Unpublished Lecture, or a Personal Communication.
Citing an Unpublished Lecture (According to the APA publication manual and Purdue's OWL):
The citation on the Reference page for the lecture notes would look like the following in APA:
Author. (year). In italics write the name or title of the lecture. Personal Collection of (the lecturer’s name), school or organization they teach for, city, state.
Berliner, A. (1959). Lecture on Reminiscences of Wundt and Leipsig.
Personal Collection of A. Berliner, University of Akron, Akron OH.
Citing a Personal Communication (According to the APA publication manual and Purdue's OWL):
Personal communications do not provide recoverable data, and are not included in the reference list. Cite personal communications in text only.
Give the initials as well as the surname of the communicator, and provide as exact a date as possible
T.K. Lutes (personal communication, April 18, 2001)