तद्विद्धि प्रणिपातेन परिप्रश्नेन सेवया। उपदेक्ष्यन्ति ते ज्ञानं ज्ञानिनस्तत्त्वदर्शिनः ॥

tad viddhi praṇipātena paripraśhnena sevayā upadekṣhyanti te jñānaṁ jñāninas tattva-darśhinaḥ

Learn thou this by discipleship, by investigation, and by service. The wise, the seers of the essence of things, will instruct thee in wisdom.

In plain words: Krishna tells Arjuna to learn this wisdom by becoming a humble student, by asking questions, and by serving. Wise people who have seen the truth will teach him.