Add '%' sign to MySQL results
CAST() might not be needed, try with and without it.

SELECT student.StudentID
    ,student.NAME
    ,CONCAT (
        cast(ROUND(Count(attendance.AttendanceID) * 100 / 6) AS CHAR(20))
        ,'%'
        ) AS Total
    ,student.WorkshopID
FROM student
LEFT JOIN attendance ON student.StudentID = attendance.StudentID
GROUP BY student.StudentID
    ,student.Name``


The ROUND function returns integer data and CAST is needed to use the result as a string parameter of CONCAT function. CHAR(20) is really arbitrary - you can use any other string data type.