It's pretty self-explanatory - the QAnon crowd thought JFK Jr. who had been dead for 23 years at that point, was secretly alive living somewhere in Pennsylvania and was planning to come back and be Trump's VP pick in 2024.
Sure, it's ridiculous nonsense from people who likely misheard or didn't realize there was a another Kennedy Jr. floating around out there, and frankly, I wouldn't put it past RFK Jr. to have been Q in the first place, but it is what it is - low information voters.