Oliver Cowdery initially wrote “obedient unto the Father”, probably because of the two preceding occurrences in the same verse of “the Father”. Almost immediately Oliver corrected the text here by crossing out “the Father” and supralinearly inserting him, all with no change in the level of ink flow. Undoubtedly, the original manuscript (which is no longer extant here) read him.
Summary: Retain in 2 Nephi 31:7 Oliver Cowdery’s corrected reading: “that he would be obedient unto him”.