As I understand you are selecting on RadComboBox, not on GridViewCell. If so, then the selection events of RadGridView will not be raised. The SelectionChanged event of RadComboBox will be raised instead.
If you want to detect a click on the cell/row, then you can subscribe for the MouseLeftButtonDown event.
sender, MouseButtonEventArgs e)
Furthermore, if you define an editor as CellTemplate, then you do not need to define such as CellEditTemplate, simply because you will be doing all the editing through the CellTemplate.
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