Yea, if thou criest after knowledge. The endeavour after Wisdom is not only to be sincere, it is also to be earnest, as appears from the "yea, if," and the verbs "crying" and "lifting up the voice," both of which frequently occur in Scripture as indicating earnestness.
This earnestness is the counterpart of that which Wisdom herself displays (see Proverbs 1:20, Proverbs 1:21). Knowledge; i.e. insight. In the original there is practically little difference between "knowledge" and "understanding" ( בִּינָה and תְּבוּנָה).
They carry on the idea expressed in "understanding" in the preceding verse, and thus throw the emphasis on the verbs. The LXX. and Vulgate, however, take "knowledge" as equivalent to σοφία, sapientia, "wisdom."
The reading of the Targum, "If thou tallest understanding thy mother," arises from reading אִם for אֵם, but is not to be preferred to the Masoretic text, as it destroys the parallelism.