A.T. Robertson Commentary Romans 11:34

"For who hath known the mind of the Lord? or who hath been his counsellor?" — Romans 11:34 (ASV)

Who hath known? (τις εγνω?). Second aorist active indicative of γινωσκω, a timeless aorist, did know, does know, will know. Quotation from Isa 40:13. Quoted already in 1 Corinthians 2:16.

Counsellor (συμβουλος). Old word from συν and βουλη. Only here in N.T.

His (αυτου). Objective genitive, counsellor to him (God). Some men seem to feel competent for the job.