The CVI event is EVENT_LEFT_CLICK. In the callback for the control or panel for which you want to check, add a case for EVENT_LEFT_CLICK. For example,
int CVICALLBACK OkCallback (int panel, int control, int event,
void *callbackData, int eventData1, int eventData2)
{
switch (event)
{
case EVENT_COMMIT:
// do something
break;
case EVENT_LEFT_CLICK:
// do something else
break;
}
return 0;
}