How to add multiple new buttons from template in a UI from C# and call on click event for a particular buttons

Rather than creating a ControlTemplate,just create a Style.Then the code would be like :

 Button btn = new Button
 btn.Style= (Style)FindResource("RoundBtn")
 grid.Children.Add(btn);
 btn.click += new EventHandler(btn_click);

 private void btn_Click(object sender, RoutedEventArgs e)
{
 }

The task of generating multiple controls for multiple items from some list is best solved using ItemsControl:

<ItemsControl Name="itemsList">
    <ItemsControl.ItemTemplate>
        <DataTemplate DataType="local:DataEntity">
            <Button Template="{StaticResource RoundBtn}" 
                    Content="{Binding Name}"
                    Click="ItemButtonClick"/>
        </DataTemplate>
    </ItemsControl.ItemTemplate>
</ItemsControl>

This ItemsControl named "itemsList" contains buttons with custom template. Each button will display one the Name of one item from list.

DataEntity is a class which contains values from db, e.g.

public class DataEntity
{
    public string Name { get; set; }
}

Items list is linked to ItemsControl via ItemsSource property (in my demo I'm doing it in window code-behind in constructor)

itemsList.ItemsSource = new ObservableCollection<DataEntity>
{
    new DataEntity { Name = "A" },
    new DataEntity { Name = "B" },
    new DataEntity { Name = "C" },
};

Buttons have click handler attached ("ItemButtonClick"). The clicked button is determined from sender argument:

private void ItemButtonClick(object sender, RoutedEventArgs e)
{
    var button = (Button)sender;
    var item = button.DataContext as DataEntity;

    MessageBox.Show("Clicked " + item.Name);
}