The 23rd Tirthankar is Bhagwan Parshvanath.

His Kalyanak‑bhoomi (main sacred birthplace land) is:

• Varanasi (Kashi / Benaras)
• In Bharat Kshetra of Jambudweep

In brief about his major kalyanaks (according to Jain tradition):

• Garbh Kalyanak – Varanasi
• Janm (Birth) Kalyanak – Varanasi
• Kevaljnan Kalyanak – Sammed Shikhar (Parshvanath Tonk)
• Moksh Kalyanak – Sammed Shikhar

So, when someone asks for the kalyanak-bhoomi of the 23rd Tirthankar, they usually mean his birthplace, which is Varanasi.