Is "Enter" a button or the keyboard key "enter"?
If it is a button, I would use the button's tapped event, the click event occurs before and you could use it too.
If it is the keyboard key then a good place to put your code is the keyup event of the TextBox
private void textBox1_KeyUp(object sender, KeyRoutedEventArgs e)
if (e.Key == Windows.System.VirtualKey.Enter)
textBlock1.Text = textBox1.Text;
All these events are fired if you use a touch interface or a mouse, so there should be no problems.