प्रकृतिं पुरुषं चैव क्षेत्रं क्षेत्रज्ञमेव च। एतद्वेदितुमिच्छामि ज्ञानं ज्ञेयं च केशव ॥

prakṛitiṁ puruṣhaṁ chaiva kṣhetraṁ kṣhetra-jñam eva cha etad veditum ichchhāmi jñānaṁ jñeyaṁ cha keśhava

Matter and Spirit, even the Field and the Knower of the Field, wisdom and that which ought to be known, these I fain would learn, O Keshava.

In plain words: Arjuna asks Krishna, whom he calls Keshava, to explain matter and spirit. He wants to know what the "Field" is and who the "Knower of the Field" is. He also asks what true wisdom is and what is most worth knowing.