<StackPanel>
        <ListBox x:Name="ttt">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <Grid>
                    
                        <Grid.ColumnDefinitions>

                            <ColumnDefinition/>
                            <ColumnDefinition/>
                          
                        </Grid.ColumnDefinitions>

                        <CheckBox Grid.Column="0" Tag="{Binding P_Idx}"> ssss</CheckBox>
                        <Label Content="{Binding P_Name}" Grid.Column="1"></Label>
                    </Grid>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
        <Button x:Name="ddds" Click="ddds_Click" Content="체크된값 가져오기"/>
    </StackPanel>

바인딩
    public class Cust
    {
        public CheckBox ccc { get; set; }
        public string P_idx { get; set; }
        public string P_Name { get; set; }
    }

        private void SetLoad()
        {
            List<Cust> li = new List<Cust>();
            li.Add(new Cust() { P_idx = "1111", P_Name = "영민" });
            li.Add(new Cust() { P_idx = "2222", P_Name = "영민2" });
            li.Add(new Cust() { P_idx = "3333", P_Name = "영민3" });
            ttt.ItemsSource = li;
        }

        private void ddds_Click(object sender, RoutedEventArgs e)
        {
            //여기서 Listbox에 checkbox에서 체크된박스에 Tag값을 읽어오고 싶습니다. 어떻게 해야 할까요? 감사합니다.

        }

---