The phrase “antonyms of what” refers to words that are opposite in meaning to the word “what”. However, the word “what” is an interrogative pronoun and doesn't really have a traditional antonym in the way that many descriptive words do.
“What” is used to ask for information about something or to inquire about the identity or nature of a thing. There isn't a single word that can be considered its opposite in the same sense that “hot” and “cold” or “big” and “small” are opposites.
If we stretch the concept a bit, perhaps words that imply certainty or a specific known entity could be seen as somewhat contrary to “what”. For example, “that” or “this” refer to specific things that are known or identified, whereas “what” asks about an unknown or unspecified thing. But this is a rather loose interpretation and not a true antonym in the traditional sense.
In conclusion, while there isn't a clear-cut antonym for “what”, we can think about words that represent the opposite end of the spectrum in terms of certainty and specificity as a way to approach the idea, but it's a somewhat unconventional analysis.