<Custom:DataGridTemplateColumn Header="Дата выдачи" Width="130" >
   <Custom:DataGridTemplateColumn.CellTemplate>
       <DataTemplate >
            <Custom:DatePicker SelectedDate="{Binding LicenseDateStart}" />
        </DataTemplate>
   </Custom:DataGridTemplateColumn.CellTemplate>
</Custom:DataGridTemplateColumn>

public ObservableCollection<OrgInfoProftraining> ListOrgInfoProftraining
    {
        get
        {
            return new ObservableCollection<OrgInfoProftraining>(_ListOrgInfoProftraining);
        }
        set
        {
            _ListOrgInfoProftraining = value.ToList();
            OnPropertyChanged("ListOrgInfoProftraining");

        }
    }