You holding your image path in json, soo try load it from resource folder.
Try like that:
private Sprite myImage;
private void myLoadGameData()
{
string myfilePath = Path.Combine(Application.streamingAssetsPath, mygameDataFileName);
if (File.Exists(myfilePath))
{
string mydataAsJson = File.ReadAllText(myfilePath);
TSGameData myloadedData = JsonUtility.FromJson<TSGameData>(mydataAsJson);
myRoundData = myloadedData.myRoundData;
myImage = Resources.Load<Sprite>(myloadedData.myRoundData.questionImage);
}
else
{
Debug.LogError("Cannot load game data!");
}
}