Psalm 78/Notes/Grammar.V. 3a.555136
From Psalms: Layer by Layer
Another possibility is to read אֲשֶׁ֣ר as a headless relative particle (as the preferred interpretation below), though with וַנֵּדָעֵ֑ם as the main clause. Such is found in the Syr. ܐܝܠܝܢ ܕܫܡܥܢ ܝܕܥܢ ܐܢܝܢ ("we know those things that we have heard," Taylor 2020, 313), and would result in a hanging topic left-dislocation of the relativized content, in light of the waw on וַנֵּדָעֵ֑ם consistently attested in Hebrew manuscripts. This is not impossible, but the relative content containing all of v. 3 has been preferred (see below).