Some languages will need to add the implicit information that Cain spoke to his brother about going to the fields. (See: [[rc://en/ta/man/translate/figs-explicit]])
God knew that Cain had killed Abel, but he asked Cain this question so that Cain would have to answer. (See: [[rc://en/ta/man/translate/figs-rquestion]])
Cain used this rhetorical question so that he would not have to tell the truth. This can be translated as a statement. AT: "I am not my brother's keeper!" or "You know that taking care of my brother is not my job!" (See: [[rc://en/ta/man/translate/figs-rquestion]])