SELECT 1 -- empty
SELECT sub.changedata -- empty
SELECT * -- not empty
FROM (
	SELECT a.objectidtype,
		a.changedata
	FROM audit AS a
	WHERE a.objectidtype = 'some_entity'
		AND a.objectid IN ('xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx')
		AND ISJSON(a.changedata) = 1
	) AS sub
OUTER APPLY OPENJSON(sub.changedata, '$.changedAttributes') AS tmp
OUTER APPLY (
	SELECT JSON_VALUE(tmp.value, '$.logicalName') AS logicalName
	) AS tmp1
WHERE tmp1.logicalName IN ('some_column')