It sounds like a QSignalMapper could be helpful here. It's designed to link multiple QObjects to a single slot and to provide context as to what was the originating source. It's generally more reliable than MarioBlueSkies sender() mechanism as you're more explicitly controlling what gets registered against the Mapper.
Something like this...
QSignalMapper *mapper = new QSignalMapper(this);
connect(mapper, SIGNAL(mapped(const QObject&)),
this, SLOT(clicked(const QObject&)));
void InputWindow::on_pushButton_ViewMilestone_clicked()
{
QTableView *viewMilestone = new QTableView;
viewMilestone->setModel(sourceMilestonesModel);
viewMilestone->setContextMenuPolicy(Qt::CustomContextMenu);
viewMilestone->resizeColumnsToContents();
viewMilestone->setMinimumWidth(getVerticalSizeOfQTableView(viewMilestone));
viewMilestone->show();
connect(viewMilestone, SIGNAL(customContextMenuRequested(const QPoint&)), signalMapper, SLOT(map()));
signalMapper->setMapping(viewMilestone, viewMilestone);
}