The printer’s manuscript originally had the plural words in the phrase “with the words of God”, but the 1830 edition had the singular word (“with the word of God”). The plural s of words in 𝓟 was later crossed out with considerably heavier ink flow. The ink looks dark, but it does not look as black as the ink Joseph Smith used for other corrections on this page. Moreover, Joseph’s corrections have left stains on the following page of 𝓟 (the opposing recto), but the crossout of the s in words has not, which argues that this correction is not Joseph Smith’s. In addition, the crossout follows Oliver Cowdery’s style for crossing out single letters, not scribe 2’s. Thus Oliver probably made this change while proofing 𝓟 against 𝓞, and so 𝓞 very likely read in the singular. As explained under Alma 5:11, either word or words is possible for the phrase “the word(s) of God”, although the singular is normal.
Summary: Accept in 3 Nephi 28:20 the singular word in “the word of God”, the 1830 reading as well as the corrected reading in 𝓟; the plural words (what scribe 2 wrote in 𝓟) is very likely an error.