Albert Barnes Commentary Job 20:3

"I have heard the reproof which putteth me to shame; And the spirit of my understanding answereth me." — Job 20:3 (ASV)

I have heard the check of my reproach - I have heard your violent and severe language reproaching us. He probably refers to what Job had said at the end of his speech (Job 19:29), that they had reason to dread the wrath of God, and that they might anticipate heavy judgments as the result of their opinions. Or it may be, as Schultens supposes, that he refers to what Job said in Job 19:2, and the rebuke that he had administered there.

Or possibly, and still more probably, I think, he may refer to what Job had said in reply to Zophar's former speech (Job 12:2), where he tauntingly says that “they were the people, and that wisdom would die with them.” The Hebrew literally is, “the correction of my shame” (כלמה מוּסר mûsâr k^elimmâ), “the correction of my shame”; that is, the chastisement or rebuke which tends to cover me with disgrace. The sense is, “You have accused me of that which is disgraceful and shameful, and under the strong feelings caused by such a charge, I cannot refrain from replying.”

And the spirit of my understanding - Meaning, perhaps, “the emotion of his mind.” The word “mind” or “soul” would better express the idea than the word “understanding”; and the word “spirit” here seems to be used in the sense of violent or agitating emotions—perhaps in allusion to the primary meaning of the word (רוּח rûach), “mind.”