Get hold of the MaintainCurrenciesCoordinator object via reflection like this:

private MaintainCurrenciesCoordinator GetCoordinator()
{
    FieldInfo fi = _form.UnderlyingControl.GetType().GetField("_oCurrenciesCoordinator", BindingFlags.Instance | BindingFlags.NonPublic);
    if(fi != null)
    {
        return (MaintainCurrenciesCoordinator) fi.GetValue(_form.UnderlyingControl);
    }
    return null;
}

Then in the form BeginSave you will be able to determine which items have been added or amended:

private void _form_BeginSave(object sender, System.ComponentModel.CancelEventArgs e)
{
    if(coordinator.IsDirty)
    {
        foreach(FinancialCurrency _fc in coordinator.Currencies)
        {
            if(_fc.IsDirty)
            {
                if(_fc.IsNew)
                {
                    MessageBox.Show($"Currency {_fc.Name} has been added");
                }
                else
                {
                    MessageBox.Show($"Currency {_fc.Name} has been edited");
                }
            }
        }
    }
}        

Get hold of the MaintainCurrenciesCoordinator object via reflection like this:

private MaintainCurrenciesCoordinator GetCoordinator()
{
    FieldInfo fi = _form.UnderlyingControl.GetType().GetField("_oCurrenciesCoordinator", BindingFlags.Instance | BindingFlags.NonPublic);
    if(fi != null)
    {
        return (MaintainCurrenciesCoordinator) fi.GetValue(_form.UnderlyingControl);
    }
    return null;
}

Then in the form BeginSave you will be able to determine which items have been added or amended:

private void _form_BeginSave(object sender, System.ComponentModel.CancelEventArgs e)
{
    if(coordinator.IsDirty)
    {
        foreach(FinancialCurrency _fc in coordinator.Currencies)
        {
            if(_fc.IsDirty)
            {
                if(_fc.IsNew)
                {
                    MessageBox.Show($"Currency {_fc.Name} has been added");
                }
                else
                {
                    MessageBox.Show($"Currency {_fc.Name} has been edited");
                }
            }
        }
    }
}        

Thank you Chris. this is a better answer. 

By the way, how to we know what is the coordinators for the page? is there any way to check it? I look through the Form Explorer but no info on coordinator

You just need to get a copy of something like .Net Reflector, or Telerik's Just Decompile and start taking things apart.

ah noted. something new I learn today.

In fact on that form, the FinancialCurrencies are the bound object, so you can use that in BeginSave