Verses with the word understandest in the Old Testament (3 verses):

Job 15:9
What knowest thou, that we know not? what understandest thou, which is not in us?

Psalms 139:2
Thou knowest my downsitting and mine uprising, thou understandest my thought afar off.

Jeremiah 5:15
Lo, I will bring a nation upon you from far, O house of Israel, saith the LORD: it is a mighty nation, it is an ancient nation, a nation whose language thou knowest not, neither understandest what they say.