God uses a rhetorical question to rebuke Cain. This can be translated as a statement. Alternate translation: "What you have done is terrible!" (See: [[rc://en/ta/man/jit/figs-rquestion]])
Abel's blood is a metonym for his death, as if it were a person calling out for God to punish Cain. Alternate translation: "Your brother's blood is like a person calling out to me to punish the person who killed him" (See: [[rc://en/ta/man/jit/figs-metonymy]])