Here in the original manuscript, Oliver Cowdery initially wrote the relative pronoun that instead of the correct which. He caught his error by erasing the that and then wrote which inline (he did not write over the erased that), thus showing that the correction was immediate. Occasionally in 𝓞 and 𝓟, Oliver mixed up the two restrictive relative pronouns that and which. For another example, see under Jacob 5:57; for a general discussion, see under which in volume 3.
Summary: Accept the immediately corrected which in Alma 27:14 (“the wilderness which divided the land of Nephi from the land of Zarahemla”).