Please avoid images when forming questions - and also do include the complete query you have tried (it seems you omitted some parts). In essence what you want to do is remove the unwanted repetition of data before you use string_agg e.g:

SELECT
      derived.StaffPreferredName
    , derived.StaffSurname
    , derived.StaffOccupEmail
    , STRING_AGG(serived.learningAreaYearLevel, ',') WITHIN GROUP ( ORDER BY learningAreaYearLevel ) AS learningAreaYearLevel
FROM (
    SELECT DISTINCT
          v.StaffPreferredName
        , v.StaffSurname
        , v.StaffOccupEmail
        , CONCAT (l.learningareacode , ' ' , sc.NormalYearLevel) AS learningAreaYearLevel
    FROM vstaffDescription AS v
    INNER JOIN mystery_table1 AS l ON v.x = l.y
    INNER JOIN mystery_table2 AS sc ON v.x = sc.y
    ) AS derived
GROUP BY
      derived.StaffPreferredName
    , derived.StaffSurname
    , derived.StaffOccupEmail

You will need to repair the missing table references and joins.

This is the full code I have used.

SELECT v.StaffPreferredName, v.StaffSurname, v.StaffOccupEmail,
STRING_AGG(CONCAT(l.Description, ': ', CAST(sc.NormalYearLevel AS VARCHAR)), ', 
') AS 'Learning Area Description' FROM vstaff v
JOIN SubjectClassStaff scf ON v.StaffID = scf.StaffID
JOIN SubjectClasses sc ON sc.FileType = scf.FileType
AND sc.FileYear = scf.FileYear
AND sc.FileSemester = scf.FileSemester
AND sc.ClassCode = scf.ClassCode
AND sc.ClassCampus = scf.ClassCampus
JOIN LearningAreas AS l ON l.FileType = sc.FileType
AND l.FileType = sc.FileType
AND sc.LearningAreaCode = l.LearningAreaCode
WHERE
sc.FileType = 'a'
AND sc.FileSemester = 3
AND sc.FileYear = 2023
AND l.LearningAreaCode <> ' '
AND sc.NormalYearLevel IS NOT NULL
GROUP BY
v.StaffPreferredName,
v.StaffSurname,
v.StaffOccupEmail
ORDER BY
v.StaffPreferredName;