gistfile1.cs

protected override bool OnServerValidate(string value)
{
    var validatorSettings = GetValidatorSettingsItem();
    Sitecore.Diagnostics.Assert.IsNotNull(validatorSettings, ValidationSettingsItemMissingMessage + ValidationSettingsItem);

    // obtain an instance of the SimpleForm
    var form = WebUtil.GetParent<SimpleForm>(this);

    // lookup the actual form item
    var formItem = Sitecore.Context.Database.Items[form.FormID];

    // obtain the WFFM field
    var countryField = formItem.Children[validatorSettings.CountryFieldId];
            
    // get its required field value from the Checkbox field
    Sitecore.Data.Fields.CheckboxField checkbox = countryField.Fields["Required"];
    if (checkbox != null)
    {
        bool isRequired = checkbox.Checked;
        // continue processing...
    }

    return base.OnServerValidate(value);
}