Hello Anton,

You can achieve this by enabling the RowSelectors behavior and setting RowNumbering to true:

<Behaviors>

   <ig:RowSelectors RowNumbering="true" Enabled="true" />

</Behaviors>

Here is a live sample: http://ko.infragistics.com/products/aspnet/sample/data-grid/row-selectors.

Let me know if you have further questions.