{
    "192.168.0.129": {
        "username": "me",
        "streaming": "Spotify",
        "name": "John",
        "email": "john@gmail.com"
    }
}

new_data = {'next_songs': ['song1', 'song2']}

with open('c.json', 'r') as json_data:
    data = json.load(json_data)

data.update(new_data)

with open('c.json', 'w') as json_data:
    json.dump(data, json_data, indent=4)

{
    "new_data": [
        "song1",
        "song2"
    ],
    "192.168.0.129": {
        "username": "me",
        "streaming": "Spotify",
        "name": "John",
        "email": "john@gmail.com"
    }
}

{
    "192.168.0.129": {
        "username": "me",
        "streaming": "Spotify",
        "name": "John",
        "email": "john@gmail.com"
        "new_data": ["song1", "song2"],
    }
}