Throughout the manga while J-man was alive (R.I.P.), he was known to have an informant that would leak information to him about Oro, the Akatsuki and other various things.
In the latest chapter we learn that Itachi decided to be a spy on the Akatsuki for Konoha.
Is it possible that Itachi was the one to leak information to Jiraiya somehow?
The only problem I see in this possibility is that this would mean that J-man would have had to know that Itachi was not really a traitor of the Uchiha clan to accept the help of Itachi. But it's possible that Itachi could have informed Jiraiya by other means:shrug: