In copying from 𝓞 to 𝓟, Oliver Cowdery initially wrote “and there shall be no king upon the land”, but then shortly thereafter he corrected the singular king by inserting an s at the end of king. The level of ink flow is only slightly heavier, which suggests that Oliver might have dipped his quill prior to correcting 𝓟. The original manuscript is not extant here; but since either reading (king or kings) will work, it is probably best to assume that the original text was in the plural and that Oliver corrected 𝓟 to agree with 𝓞.
Summary: Maintain the plural kings in 2 Nephi 10:11; although the plural is the corrected reading in 𝓟, the correction appears to be nearly immediate; 𝓞 itself probably read in the plural.