Hi Haythem,
The best is to create an Operator Interface (several LV examples are given with your TestStand installation).
In these OI you'll see that you can register to events that the API expose.
UIMessages and UserMessages are the callbacks that you're searching for. Once added to your Register Events node, you create a VI Callback that will be fired when the TS engine fires up UIMessages.
Then you can decode the message parameters to share it into your LV application thanks to LV User Events or FIFOs.
Really the start point for what you want to do are the Operator Interfaces.