Yea unless he got his from them kara folk(if they have one)
Nope. Boruto never got a seal from killing a God.Now, I don't read this new garbage manga, but doesn't the fact that Kawaki has a tattoo mean that he's defeated "a God", "the same" as Boruto?
Momoshiki was interested in him after his death, then he gave him a seal. It was never explained on his motivations either.
Still a mystery
Kawaki and the new guy named Jigen have the seals, so I'm sure they probably got theirs out of being interesting as well.