The phrase is an interrogative noun clause, functioning as a direct inquiry. Its central grammatical component is the proper noun "Patriots' Day." The clause's purpose is to request a specific data point: the calendar date for this holiday within the current annual cycle.
Patriots' Day is a state holiday observed in Massachusetts and Maine, commemorating the anniversary of the Battles of Lexington and Concord. Its date is legally defined not as a fixed number but as the third Monday in April. For the current year, 2024, this observance falls on April 15.
The practical application of this rule means the holiday's date is variable and changes each year, unlike holidays set to a specific calendar day such as July 4th. This floating nature necessitates an annual confirmation to determine the exact date, as it will always fall on a Monday but can range from the 15th to the 21st of the month.
