Create a table (Holiday) with two columns, and enter holiday dates and country where they are observed.  Both columns should be the Clustered PK.  If the same holiday is observed in several countries, add a record listing date and (each) country where it is observed.

To find workdays, first exclude weekends (several options are available), and deduct amount of holidays (DECLARE @FirstDate DATETIME, @LastDate DATETIME, @Country VARCHAR (25)

SELECT COUNT(*) FROM Holiday WHERE data BETWEEN @FirstDate AND @LastDate and country = @Country)