Yes, that's right, it does begin with JN. It's from the Indo-European root GNO- meaning 'know, knowledge': which becomes the KNO- of the English words, and is the GNO- of Greek gnosis, Gnostic etc.
The second letter is a NY sound, as in Spanish. Altogether not easy to pronounce. (I believe modern Sanskritists give up on the original DYNY- sound and just make it some simpler combination, such as GY- or GNY-.)