Answer

Posh Dasam means the 10th day of the Jain month of Posh.

To tell you the exact date, I need to know:

• Which year?
• Which calendar tradition you follow — Gujarati/Jain calendar may vary by location and Panchang.

Explanation

In Jain tradition, dates like Posh Dasam are based on the lunar calendar, so they do not fall on the same English calendar date every year.

Takeaway

Please tell me the year, and I can help identify when Posh Dasam falls.