SELECT [Year], [Month], sum([Benefits Rating]) AS [Benefits Rating], sum([Facilities Rating]) AS [Facilities Rating]
  FROM (...... your origin query ......) X
  GROUP BY [Year], [Month]

SELECT     DATEPART(year, q.attempted_date) AS Year, DATENAME(MM, q.attempted_date) AS Month, 
                      AVG(CASE WHEN w.category_id = 1 THEN CAST(SUBSTRING(a.answer, 4, 1) AS int) ELSE NULL END) AS [Average Benefits Rating], 
                      AVG(CASE WHEN w.category_id = 2 THEN CAST(SUBSTRING(a.answer, 4, 1) AS int) ELSE NULL END) AS [Average Facilities Rating]
FROM         questionnaire AS q INNER JOIN
                      employee AS e ON q.employee_id = e.employee_number INNER JOIN
                      answer AS a ON e.id = a.employee_id INNER JOIN
                      question AS w ON a.question_id = w.id
WHERE     (w.question_type = 1) AND (a.answer <> 'ansNA') AND (q.attempted_date IS NOT NULL)
GROUP BY DATEPART(year, q.attempted_date), DATENAME(MM, q.attempted_date)
ORDER BY Year, Month DESC