Here the 1841 British edition omitted the definite article the before truth. Although “the knowledge of truth” is theoretically possible, the Book of Mormon text has only “the knowledge of the truth” (15 times), including these two other examples in this same chapter of Alma:
Here in Alma 17:2, the immediately following LDS edition (1849) restored the definite article the.
Summary: Maintain in Alma 17:2 the expected the before truth in “the knowledge of the truth”.