How to check whether json object has some property

Just use obj["proprty_name"]. If the property doesn't exist, it returns null

if(obj["proprty_name"] != null){
    // do something
}

You can try like this:

IDictionary<string, JToken> dict = x;
if (dict.ContainsKey("some_key"))

since JSONObject implements IDictionary<string, JToken>. You can refer MSDN for details