You have to cast
sender
to its real class or one of the interfaces it implements to use methods and properties.
Here is one way to do it:
private void MyClick(object sender, GestureEventArgs e)
{
TextBlock txt = sender as TextBlock;
if( txt == null )
{
throw new ArgumentException("MyClick needs first parameter to be a TextBlock");
}
string whatEver = txt.Text;
}