Answer

The Janma Kalyanak place in Varanasi is traditionally associated with Bhagwan Parshvanath, the 23rd Tirthankar.

It is commonly identified with the Jain tirth at:

Bhelupur, Varanasi, Uttar Pradesh, India

Explanation

In Jain tradition, Varanasi is the birthplace of Bhagwan Parshvanath. His Janma Kalyanak is especially connected with the sacred Jain site at Bhelupur.

Takeaway

If you are planning a visit, you can ask locally for Shri Parshvanath Janmabhoomi Jain Mandir, Bhelupur, Varanasi.