Does lord Krishna talk about Kundalini anywhere in Bhagwat Gita or somewhere else ?
Krishna Paramatma doesn't talk of Kundalini directly but in two cases, he has hinted about process of Kundalini in indirect manner where he says to fix the Prana in between eyebrows and remember the supreme in full devotion to attain the lotus feet of the Lord.
Bhagavad Gita verse 8.10: prayana-kale manasacalena
bhaktya yukto yoga-balena caiva
bhruvor madhye pranam avesya samyak
sa tam param purusam upaiti divyam
One who, at the time of death, fixes his life air between the eyebrows and in full devotion engages himself in remembering the Supreme Lord, will certainly attain to the Supreme Personality of Godhead.
In another instance also Krishna talks about the knowledge of closing all the doors of the body and fixing life air at the top of head. This is also another indirect knowledge of Kundalini where it is made to rise to top of head by piercing through various chakras.
Bhagavad Gita 8.12 sarva-dvarani samyamya
mano hrdi nirudhya ca
murdhny adhayatmanah pranam
The yogic situation is that of detachment from all sensual engagements. Closing all the doors of the senses and fixing the mind on the heart and the life air at the top of the head, one establishes himself in yoga.
These are the instances where Krishna gives the knowledge of Kundalini indirectly in different perspective!
Yes, in Uttar Geeta, another conversation between Krishna and Arjuna
- Like the backbone of a vina or harp, the long tract of bone with many joints that stretches from the seat right up to the head of a human being is called the merudanda (spinal cord).
- There is a minute aperture or hole that passes right through this merudanda from the muladhara to the head; it is through this hole that there passes a nadi which the yogins call the brahmanadi or sushumna.
- Sushumna is a fine nerve that passes between the ida and pingala; from this sushumna all the jnananadis [sensory nerves] take their birth. Hence it is called the jnananadi.
- The sun, the moon and the other devatas, the fourteen lokas of Bhur, Bhuvas etc., the ten Dikas [directions], east, west, etc., the sacred places, the seven oceans, the Himalaya and other mountains, the seven islands of jambu, etc., the seven sacred rivers, Ganga, etc., the four Vedas, all the sacred philosophies, the sixteen vowels and twenty-four consonants, the Gayatri and other sacred mantras, the eighteen Puranas and all the Upapuranas included, the three gunas, mahat itself, the root of all the jivas, the jivas and their atman, the ten breaths, the whole world, in fact, consisting of all these, exists in the sushumna.
- As various nadis have sprung up from the sushumna, the receptacle for the inner soul of all jivas, and are stretched out in all directions of the physical body, therefore it is considered to be like a huge tree reversed. The tattvajnanins alone are able to walk on every branch of this tree by the help of pranavayu.
- The lower portion or the sole of the foot, is called Atala; the upper portion or the top is called Vitala; the upper part of the joint between the leg and the foot is called Nitala, and the knee is called Sutala.
- The lower portion of the thigh is called Mahatala; the upper portion of it is called Rasatala, and the loin is termed Talatala. In this way it is right to know the seven Patalas that exist in the human body.
In the Patala where the serpents live in coils, and below the navel, is the place known by the name of Bhojindra. This dreadful place, like a burning hell and doomsday fire, is termed Mahapatala; in this sphere the Eternal, known by the name of jiva, displays itself in serpentine coils like a circle.
In the heart dwells the Maharloka, the Janaloka exists in the throat, the Taparloka between the two eyebrows, whilst the Sattvaloka exists in the head.