Print the response from GSM shield
I have only worked with the SIMCOM series of GSM modules like the SIM900 and the SIM808. Here is a sample of the kind of code you should be looking at using.
It will send one "AT" to the GSM module and then it will spit out the result in the serial monitor.

void setup()
{
  Serial.begin(115200);
  int bytesSent = Serial.write(“AT\r\n”); //send "AT" and send the end of line characters to signify end of the command
 }

 void loop()
{
   if (Serial.available() &gt; 0) {
            // read the incoming byte:
            incomingByte = Serial.read();
    }
}