The second wherefore in this long sentence was deleted by Joseph Smith in his editing for the 1837 edition. The original repetition of wherefore is helpful because it brings the reader back to the sentence-initial wherefore after a long intervening parenthetical clause. For additional examples of this kind of repetition, see under 2 Nephi 5:21. The critical text will restore the redundancy of the original text here in 2 Nephi 6:11.
Summary: Restore in 2 Nephi 6:11 the repeated wherefore that Joseph Smith deleted in his editing for the 1837 edition.