Jambudwip Kshetra is in Madhya-lok according to Jain cosmology.

It is the central island-continent in the middle of the Jain universe and is surrounded by Lavana Samudra. It is the realm where human life, karma, and dharma are especially significant, and Bharat Kshetra and Airavat Kshetra are parts of Jambudwip.

In simple words: Jambudwip is the central terrestrial region of the Jain universe.