SQL Server Dynamic Pivot query error: Must declare the scalar variable

Dear @stabeach, 

You can't concatenate an int to a string,

Change  

WHERE tblDutyGroup.GrNo =  @Sql

to 

WHERE tblDutyGroup.GrNo =  ' + CONVERT(VARCHAR(12), @Sql)+ '

Please refer below article, it might help you

https://stackoverflow.com/questions/7181976/must-declare-the-scalar-variable

Try by using Below query.

Declare @sql INT
SET @sql = 2
DECLARE @DynamicPivotQuery AS NVARCHAR(MAX)
DECLARE @ColumnName AS NVARCHAR(MAX)
DECLARE @SelectColumnName AS NVARCHAR(MAX)
SELECT @ColumnName=  ISNULL(@ColumnName + ',','')  + QUOTENAME(REPLACE(CONVERT(NVARCHAR,SDate, 106), ' ', '-'))
FROM (SELECT DISTINCT SDate FROM  tblDuty WHERE SDate BETWEEN GETDATE() AND DATEADD(d, 7, GETDATE())) AS Week
SELECT @SelectColumnName
    = ISNULL(@SelectColumnName + ',','')
    + 'ISNULL(' + QUOTENAME(REPLACE(CONVERT(NVARCHAR,SDate, 106), ' ', '-')) + ', 0) AS '
    + QUOTENAME(REPLACE(CONVERT(NVARCHAR,SDate, 106), ' ', '-'))
FROM (SELECT DISTINCT SDate FROM tblDuty WHERE SDate BETWEEN GETDATE() AND DATEADD(d, 7, GETDATE())) AS Week
SET @DynamicPivotQuery =
N'SELECT StIdNo, dbo.InitCap(EmpName) As EmpName, dbo.InitCap(Job) AS Job,  ' + @SelectColumnName +
'FROM
(
SELECT REPLACE(CONVERT(CHAR(15), SDate, 106),'' '',''-'')  AS SDate, StIdNo, EmpName, Job,  ShiftId FROM tblDuty INNER JOIN
tblSessions ON tblDuty.SessonId = tblSessions.SSId INNER JOIN
tblEmpENg ON tblEmpEng.EmpNo = tblDuty.StIdNo INNER JOIN
tblDutyStaffs ON tblDutyStaffs.StaffId = tblDuty.StIdNo INNER JOIN
tblDutyGroup ON tblDutyGroup.GrNo = tblDutyStaffs.ShiftGrId
AND tblDutyGroup.GrNo = '+ CONVERT(VARCHAR(2), @Sql) +'
GROUP BY StIdNo,  SDate,  ShiftId, SessonId, EmpName, Job
) x
PIVOT
    (
        SUM(x.ShiftId) for x.SDate in (' + @ColumnName + ')
    ) P ORDER BY EmpName ASC'
EXEC(@DynamicPivotQuery);