If you mean Pau Dasam / Posh Dasham (Poṣa-daśamī), it is the Jain observance of Bhagwan Parshvanath’s Janam Kalyanak and is kept on Paush Krishna Dashami. The exact Gregorian date in 2026 can vary by regional Jain panchang and by Digambar/Shwetambar tradition, so it should be confirmed from your local temple calendar. ( jainknowledge.com)

I could verify the tradition and tithi, but I did not find one single universally fixed 2026 date from a reliable Jain source.