SQL Server 2019

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DECLARE @json NVARCHAR(MAX) = N'[  
  {
      "id": 2,
      "info": {
          "name": "John",
          "surname": "Smith",
          "age": 25
        }
    },
    {
        "id": 5,
        "info": {
            "name": "Jane",
            "surname": "Smith",
            "skills": [
                {
                    "name": "SQL",
                    "group": "SQLnerds"
                },
                {
                    "name": "C#",
                    "group": "C#nerds"
                },
                {
                    "name": "Azure",
                    "group": "Azurenerds"
                }
            ]
        },
        "dob": "2005-11-04T12:00:00"
    }  
]';

SELECT v.id,
      v.firstName,
      v.lastName,
      v.age,
      v.dateOfBirth,
      JSON_VALUE(v.skills, '$[0].name') as singleskill,
      v.skills,
      STRING_AGG( v2.skill_name, ',') as skillstring
FROM OPENJSON(@json)  
  WITH (
    id INT '$.id',
    firstName NVARCHAR(50) '$.info.name',
    lastName NVARCHAR(50) '$.info.surname',  
    age INT '$.info.age',
    dateOfBirth DATETIME2 '$.dob',
    skills NVARCHAR(MAX) '$.info.skills' AS JSON
) as v 
OUTER APPLY OPENJSON(skills) WITH (
   skill_name NVARCHAR(100) '$.name' 
) as v2
GROUP BY  v.id, v.firstName, v.lastName, v.age, v.dateOfBirth, v.skills

;

id	firstName	lastName	age	dateOfBirth	singleskill	skills	skillstring
2	John	Smith	25	null	null	null	null
5	Jane	Smith	null	2005-11-04 12:00:00.0000000	SQL	[ { "name": "SQL", "group": "SQLnerds" }, { "name": "C#", "group": "C#nerds" }, { "name": "Azure", "group": "Azurenerds" } ]	SQL,C#,Azure