Q. How do I cite a PowerPoint presentation from my instructor in MLA format on my works cited page?

It depends on if the PowerPoint was presented in class as part of a lecture, or if you were given access to a PowerPoint by your instructor.

PowerPoint During Lecture
If a a PowerPoint was used during your instructor's lecture,

Author last, first. "Lecture title." Location of lecture, date, lecture

example :  Johnson, Amy. "The History of China." College of the Mainland. 10 May 2014. Lecture

PowerPoint Viewed Outside Class
I your instructor just a gave you  a link or access to the PowerPoint and you viewed it outside of class you'd cite it as a file. Here are the basics:

Author last, first. "PowerPoint title." creation date, Microsoft PowerPoint file

example: Johnson, Amy. "The History of China." 3 May 2014, PowerPoint file