Q. 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I would advise you to consult with your professor to determine the type of source the guest speaker is, an Unpublished Lecture, or a Personal Communication.
Citing an Unpublished Lecture (according to the APA publication manual and Purdue's OWL): https://owl.purdue.edu/owl/research_and_citation/apa_style/apa_formatting_and_style_guide/reference_list_other_non_print_sources.html (>>Individual Presentation in a Larger Symposium/Panel)
Citing a Personal Communication (according to the APA blog): https://apastyle.apa.org/style-grammar-guidelines/citations/personal-communications