Hello Fábio,
NComboBox has property called EditControl which is TextBox control. You can use the autocomplete functionality of that control.
Please note that this TextBox control is initialized only when NComboBox.Editable is true!
For NCommboBoxCommand is the same, only difference is that you need to set EditControl as follows : NComboBoxCommand.HostedControl.EditControl.
Best Regards,
Nevron Support Team