SQL SERVER – UDF – Get the Day of the Week Function

Create function running following scripｔ:
CREATE FUNCTION dbo.udf_DayOfWeek(@dtDate DATETIME)
RETURNS VARCHAR(10)
AS
BEGIN
DECLARE @rtDayofWeek VARCHAR(10)
SELECT @rtDayofWeek = CASE DATEPART(weekday,@dtDate)
WHEN 1 THEN 'Sunday'
WHEN 2 THEN 'Monday'
WHEN 3 THEN 'Tuesday'
WHEN 4 THEN 'Wednesday'
WHEN 5 THEN 'Thursday'
WHEN 6 THEN 'Friday'
WHEN 7 THEN 'Saturday'
END
RETURN (@rtDayofWeek)
END
GO

Call this function like this:
SELECT dbo.udf_DayOfWeek(GETDATE()) AS DayOfWeek
ResultSet:
DayOfWeek
———-
Monday

Method 2: (This is update from comments I received below)
SELECT DATENAME(dw, GETDATE())