There is no AUX port on the AS-GT mount, so you need to get an adapter to provide an AUX port for the mount. Celestron’s AUX port accessory plugs into the AS-GT hand control (HC) port and allows you to split that port so it can be used for the hand control and the GPS simultaneously.
Alternatively, go to any electronics supply store and purchase a phone line splitter. Plug it into the HC port and allow you to attach the GPS accessory and the hand control at the same time. All you need to do is make sure the connector you purchase is the correct size as they come in four-pin and six-pin varieties. You need the six-pin adapter.