public class Utils
{
public static void ShowHint(Grid grid, string textBlockName, string hint)
        {
            TextBlock textblock = grid.FindName(textBlockName) as TextBlock;
            ToolTip toolTip = new ToolTip()
            {
                MaxWidth = 400,
            };
            toolTip.Template = new ControlTemplate();
            toolTip.Content = new TextBox()
            {
                FontFamily = new FontFamily("Georgia"),
                FontSize = 14,
                Text = hint,
                TextWrapping = TextWrapping.Wrap
            };
            ToolTipService.SetToolTip(textblock, toolTip);
        }
}

...
Utils.ShowHint(myGrid, "Text_Block", "Show me hint.");
...