This is a doublet. Lamech said basically the same thing twice to show how important it was that they listen to what he was about to say. (See: [[rc://en/ta/man/translate/figs-doublet]])
This could be translated "my word" or "my speaking."
## a man for wounding me, a young man for bruising me ##
This is a doublet. It refers to only one person.
## for wounding me ##
"because he wounded me" or "because he hurt me"
## If Cain will be avenged sevenfold ##
This can be translated with an active verb. "If God will avenge Cain sevenfold" or "If anyone who kills Cain will be punished seven times as much as Cain was punished." (See: [[rc://en/ta/man/translate/figs-activepassive]])
## truly Lamech seventy and sevenfold ##
"truly I will be avenged seventy-seven times as much" or "truly whoever kills me will be punished seventy-seven times as much."