Here scribe 2 of 𝓟 wrote “and now he saith that he hath not spoken it”, which is not a difficult reading when considered in isolation. Oliver Cowdery, when he proofed 𝓟 against 𝓞, supplied the preposition against, which makes sense within the larger context. Note that earlier in verse 26 Amulek says “ye say that I have spoken against your law but I have not”. Undoubtedly 𝓞 had the preposition against also in verse 28.
Summary: Accept in Alma 10:28 Oliver Cowdery’s corrected reading with the preposition against (“he hath not spoken against it”).