<Grid>
    <Button Name="ButtonOne"/>
</Grid>

public class CodeBehind : MonoBehaviour
{
    private Button _button;

    private void Start()
    {
        // get the Noesis component
         var noesisGui = GetComponent<NoesisGUIPanel>();
        // get the root object (grid)
         var grid = _noesisGui.GetRoot<Grid>();
        // get the button
        _button = grid.FindName<Button>("ButtonOne");
        // attach a delegate method
        _button.Click += ButtonOneClick;
    }

    private void ButtonOneClick(BaseComponent sender, RoutedEventArgs args)
    {
        // do stuff
    }
}

<Button Click="OnClick"/>