If you use textblock in DataTemplate, such as follow:

The Textblock can't be find when use Coded UI Test, Label is OK.

We need to custom textblock, as follow, and use as above.

public class AutomatableTextBlock : TextBlock    {        protected override AutomationPeer OnCreateAutomationPeer()        {            return new AutomatableTextBlockAutomationPeer(this);        }        class AutomatableTextBlockAutomationPeer : TextBlockAutomationPeer        {            public AutomatableTextBlockAutomationPeer(TextBlock owner)                : base(owner)            { }            protected override bool IsControlElementCore()            { return true; }        }    }

Details refer: