When do you learn soul eaters real last name is Evans?

Soul Eater's real last name, Evans, is never explicitly stated in the manga or anime.

The character's full name, Soul Eater Evans, is only mentioned in the *Soul Eater: Not!** spin-off manga, which takes place after the events of the main story.

Therefore, the first time readers or viewers learn Soul Eater's full name, including his last name, is in the *Soul Eater: Not!** spin-off.