The teacher said: 'Friend, you shine like one who knows Brahman. Who then has taught you?' He replied: 'Not men. But you only, Sir, I wish, should teach me;

In plain words: The teacher sees that Satyakama's face glows like someone who knows Brahman and asks who taught him. Satyakama says beings other than humans taught him, but he wants his teacher to be the one who teaches him.