Here the 1905 LDS edition added the preposition in. This change may have been a conscious emendation since one might think that Jerusalem was not the land of the Nephites’ forefathers but was in that land. The 1911 LDS edition maintained the intrusive in in this passage, but the 1920 edition removed it from the LDS text. Jesus was born in Bethlehem, which would have been in the land of Jerusalem (as many Book of Mormon commentators have pointed out) but not within the city itself. Thus the 1905 reading is by implication wrong since it would normally be read as meaning that Jesus was born in the city of Jerusalem.
The Book of Mormon frequently refers to Jerusalem as “the land of Jerusalem” (45 times, including here in Alma 7:10). There are 9 references to “the city of Jerusalem” plus 98 references to Jerusalem without any specific use of the word city or land (and many of these could be interpreted as referring to the land of Jerusalem). The text has 18 other cases of the prepositional phrase “at Jerusalem”, and many of these could refer to the land of Jerusalem.
In accord with the earliest textual sources as well as usage elsewhere in the Book of Mormon, the critical text will retain the more difficult but accurate reading in Alma 7:10 without the preposition in.
Summary: Maintain the original text in Alma 7:10, which refers to the Son of God as having been born in the land of Jerusalem: “he shall be born of Mary at Jerusalem which is the land of our forefathers”.