Here the 1892 RLDS edition accidentally skipped the linking verb is, probably because the preceding word, this, ends in the same letters, is. The result was that this edition accidentally created a Hebraism, so to speak. (In Hebrew this passage would be expressed without the be verb.) What is surprising here is that this omission was carried over into the subsequent RLDS edition (1908). The 1953 RLDS edition finally restored the is. This typo provides one more example of how Hebraistic-like readings may sometimes accidentally enter the text. For another example, see 1 Nephi 17:11, where the 1874 RLDS edition introduced an extra and that could be interpreted as a primitive Hebraism if one didn’t know the history of the text.
Summary: Maintain the linking verb is in 2 Nephi 32:6 (“behold this is the doctrine of Christ”).