It was part of his inaugural address in 1961. I watched it live on TV. It was his own original utterance (it wasn’t a quote until after he said it for the first time). If he had been quoting someone else, he would have named the source. People have been quoting him, though, ever since.

I have to correct a slight misquote in your Q, since we’re talking about exact language: he said, “Ask not what your country can do for you – ask what you can do for your country.” (You have an extra “for.”)

I wasn’t born then, but I’ve always been told it was JFK who originally spoke them. I did a quick search and can find nothing to disprove this. I would assume that if there was any chance that someone else had uttered it first that Fox would have had a field day with that news

No one doubts that those were JFK’s words, any more than they doubt that Abraham Lincoln’s words or Franklin Roosevelt’s were his own. Why would anyone even bring up plagiarism? It isn’t an issue.

As for Fox News, it’s a recent phenomenon. The channel was launched in 1996. There was nothing like it in 1960. In those days of network broadcasting, all three commercial television networks (NBC, CBS, and ABC) had real news coverage with respected anchors and journalists. “Educational television,” the forerunner of PBS, was just barely getting started then and wasn’t doing regular newscasts. None of them was doing anything remotely resembling one-sided political propaganda or attack-as-entertainment.

@Jeruba Unless he edited it and it’s gone, I see no extra “for”.

He did. He edited it after I posted my comment. It originally said “Ask not for what your country can do for you.” By then it was too late to edit mine, so I just look like I didn’t know what I was talking about.

@Jeruba Lol Not to worry. I think most people will guess that it was edited – and now they will know! ;o)

Historic Analogues : A work that resembles one found in another work.
JKF was an avid reader of literature of which famous quotes were in later centuries restated.

( JFK wasn’t the first Politician to use a quote and change it into his own words as numerous
Politicians and leaders have done so in the past).

Oliver Wendal Holmes in 1884 and others before him and after him .

Here is a link to explain:

https://anothercenturyblog.com/2017/04/28/ask-what-you-can-do-for-your-country-the-history-of-an-inaugural-sentence/

Near Arthur Schlesingers photograph is that paragraph that show these ideas that were reused in their own words as many leaders do in the present as well and in thr future many will also.