SQL Server 2019

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declare @json nvarchar(max)=
'
[{
        "images": [{
            "key": "c:\\stapler\\booktest\\gray00024.jp2",
            "imageNumber": 1
        }],
        "instrumentNumber": 94109416
    },
    {
        "images": [{
                "key": "c:\\stapler\\booktest\\gray00025.jp2",
                "imageNumber": 1
            },
            {
                "key": "c:\\stapler\\booktest\\gray00026.jp2",
                "imageNumber": 2
            }
        ],
        "instrumentNumber": 94109417
    },
    {
        "images": [{
                "key": "c:\\stapler\\booktest\\gray00027.jp2",
                "imageNumber": 1
            },
            {
                "key": "c:\\stapler\\booktest\\gray00028.jp2",
                "imageNumber": 2
            }
        ],
        "instrumentNumber": 94109418
    }
]'
;
select a.instrumentNumber, b.skey, b.imageNumber
from openjson (@json)
with (
  instrumentNumber nvarchar(100)  '$.instrumentNumber',
  images nvarchar(max) as json
) a
cross apply openjson (a.images)
with (
  skey nvarchar(500) '$.key',
  imageNumber nvarchar(500) '$.imageNumber'
) b

instrumentNumber	skey	imageNumber
94109416	c:\stapler\booktest\gray00024.jp2	1
94109417	c:\stapler\booktest\gray00025.jp2	1
94109417	c:\stapler\booktest\gray00026.jp2	2
94109418	c:\stapler\booktest\gray00027.jp2	1
94109418	c:\stapler\booktest\gray00028.jp2	2