The structure of the discourse suggests that the 1830 typesetter’s emendation of give (the reading in 𝓟) to gave (the 1830 reading) parallels the preceding use of gave in this passage:
and gave unto Moses power that he should heal the nations
and also gave him power that he should smite the rock
The occurrence of the also especially supports the use of gave. Similar instances of “gave … also gave” are found elsewhere in the text:
Furthermore, scribal mix-ups between gave and give are possible. Here are three examples of this error in the original manuscript, although Oliver Cowdery is not responsible for any of these scribal errors:
My own sense is that the 1830 typesetter’s emendation is probably correct here in 2 Nephi 25:20 since it is supported by the resulting parallelism of “gave … also gave” (which is found elsewhere in the text).
One possible explanation for the give in 𝓟 for 2 Nephi 25:20 is that Oliver Cowdery, when copying from 𝓞 into 𝓟, was influenced by the infinitive form raise in the preceding clause (“which he did raise up before them”)—that is, Oliver ended up writing give as if the text read “did give”. (It is also possible that such an error could have been introduced by Joseph Smith himself as he dictated the text to Oliver.) This interpretation suggests another possible reading for the original text here in 2 Nephi 25:20—namely, “and did also give him power” (or “and also did give him power”, depending on where the did would have originally occurred). Accidentally omitting a did in 2 Nephi 25:20 seems quite possible since elsewhere such an error sometimes occurred during the copying of 𝓞 into 𝓟:
Summary: Accept in 2 Nephi 25:20 the 1830 typesetter’s emendation of give to gave; this conjecture reinforces the parallelism between the two conjoined predicates “gave unto Moses power” and “also gave him power”.