Here scribe 2 of 𝓞 wrote seethest, an obvious conflation of an initial seeth followed by the correct -est ending. Oliver Cowdery corrected this scribal error in the original manuscript itself by crossing out the entire word and supralinearly inserting the correct seest. Here we have one more example of the scribal tendency to overextend the biblical ending -eth. Undoubtedly the original reading here in 1 Nephi 13:28 is seest, not seeth. See the discussion under 1 Nephi 11:2 as well as the more general discussion under infl al endings in volume 3.
Summary: The correct reading in 1 Nephi 13:28 is “thou seest” (which is Oliver Cowdery’s correction of the impossible “thou seethest”).