The original manuscript undoubtedly had the repeated of here in 3 Nephi 3:19 (“the spirit of revelation and also of prophecy”). Both the 1830 edition and the printer’s manuscript have the repeated of. The 1837 edition (probably accidentally) omitted the repeated of. The Book of Mormon text has examples of this construction both with and without the repeated of:
There is one example that involves a different preposition, and in that case the preposition is repeated:
Since either reading is theoretically possible for 3 Nephi 3:19, the repeated of should be restored. It should also be noted that the phrase “and also of X” occurs 27 other places in the Book of Mormon, so there is nothing wrong with having also before the repeated of.
Summary: Restore in 3 Nephi 3:19 the repeated of in “the spirit of revelation and also of prophecy”, the reading of both 𝓟 and the 1830 edition.