It starts at a specific point in the manga, but I can't recall exactly without looking it up. You might want to check some manga forums or dedicated fan sites for the precise chapter.
They are. Edits in comic books could range from color adjustments to reworking dialogues or adding/removing panels to better suit the overall theme and flow.
Sukuna does die in the manga. The way it happens is quite dramatic and ties in with many other elements of the story, adding depth and tension to the overall narrative.
Well, for copy editing a novel, you need to focus on language accuracy. That means correcting punctuation, fixing word usage, and ensuring the sentences are structured properly. Another important aspect is to maintain the author's voice while improving the clarity and flow of the text.