It depends on how closely the movie followed the manga. But a good place to start might be the next major story arc or the chapter that directly follows the movie's ending. Check online manga guides for specific details.
You can continue the JJK manga from the chapter where the anime ended. Usually, you can find this information on manga-related forums or fan communities.
I'd suggest starting from the point where the anime ended. That way, you won't miss any new developments and can continue the story seamlessly. But if you want a more comprehensive experience, starting from the very first chapter is also a good choice.