#include <QApplication>
#include <QDialog>
#include <QDebug>

class myEventFilter: public QObject
{
  public:
  myEventFilter() : QObject() {}
  ~myEventFilter(){}
  bool eventFilter(QObject* object,QEvent* event)
  {
      if( event->type() == QEvent::EnterWhatsThisMode)
          qDebug() << "QEvent::EnterWhatsThisMode";
    return QObject::eventFilter(object,event);
  }
};

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    a.installEventFilter(new myEventFilter());
    QDialog d;
    d.setWhatsThis("Lorem Ipsum..");
    d.show();
    return a.exec();
}