SELECT 
  [MEDX_Nomenclature].[Key],
  (
    SELECT
	  [SpecimenCode]
    FROM
      [MEDX_NomenclatureSpecimen]
   WHERE
	  [MEDX_NomenclatureSpecimen].[NomenclatureKey] = [MEDX_Nomenclature].[Key]
    FOR JSON PATH
  ) AS [Test]
FROM
  [MEDX_Nomenclature]
WHERE
  [Key] IN (560, 561, 562)

SELECT 
'[' +
STUFF(
	(
		SELECT 
			[text()] = ',"' + Item + '"'
		FROM
		(
			SELECT 'A' AS Item
			UNION ALL SELECT 'B' AS Item
			UNION ALL SELECT 'C' AS Item
		) AS Q
		FOR XML PATH('')
	),
	1,1,''
)
+ ']'