知 here is a figure named Knowledge, not the verb 'to know'. The chapter opens with him wandering north and asking how to know the Dao. One sage gives no answer at all, and the Yellow Emperor says that one was right:
知者不言，
言者不知 'those who know do not speak; those who speak do not know'. The chapter also holds
天地有大美而不言 'heaven and earth have great beauty but do not speak of it'.
