। स्वरूपनिष्ठा ॥
In plain words
How could knowledge appear if there were no ignorance? Without knowledge, would ignorance appear? To enquire whose these two are, and so to abide in one's original nature: that is knowledge of the highest truth.
Word for word
How would knowledge appear, if there were not ignorance? Without knowledge, would ignorance appear? Having enquired, 'And whose are the two?', abiding in one's original nature is knowledge of the highest truth.