What is Jnana yoga?

It's the path of knowledge. It's for intleggent people, who don't like physical action. It's for people who like to read, who like philosophy, who like academically study. But Bhakti and Karma is must too. Janana, Bhakti and Karma is 3 corners of one triangle, If for you east to start from knowledge part, do it. Karma and Bhakti will come later.

Jnana is Sanskrit for “knowledge or wisdom” and Jnana Yoga is the path of attaining knowledge of the true nature of reality through the practice of meditation, self-inquiry, and contemplation. Jnana Yoga can be defined as the “awareness of absolute consciousness,” and is a comprehensive practice of self-study (Svadhyaya).

In Jnana yoga, the mind is used to inquire into its own nature and to transcend the mind’s identification with its thoughts and ego. The fundamental goal of Jnana yoga is to become liberated from the illusionary world of maya (self-limiting thoughts and perceptions) and to achieve the union of the inner Self (Atman) with the oneness of all life (Brahman). This is achieved by steadfastly practicing the mental techniques of self-questioning, reflection and conscious illumination that are defined in the Four Pillars of Knowledge. Jnana Yoga utilizes a one-pointed meditation on a single question of self-inquiry to remove the veils of illusion created by your concepts, world views, and perceptions. This practice allows you to realize the temporary and illusionary nature of maya and to see the oneness of all things.

Jnaya Yoga Or Dnyana Yoga is the most difficult path requiring tremendous strength of will and intellect. Jnana in Sanskrut meaning 'Knowledge'. Jnana yoga leads the practitioner to experience his unity with the God or supreme reality directly by breaking the glass dessolving the veils of egnorance.
Qualification for Jnana yoga is 'Sadhana Chatusthya' 1. Vivek 2. Vairagya 3. Shatasamapathi (Six Attributes) 4. Mumukshutva