For adding a delete prompt on a datatable (looks like its going to be a datagrid in UI), you would need to bind the javascript to prompt for this alert during the ItemDataBound/RowDataBound event of the datagrid.
In this event, while the data is binded row by row - add something like:
LinkButton l = (LinkButton)e.Row.FindControl("LinkButton1");
l.Attributes.Add("onclick", "javascript:return " +
"confirm('Are you sure you want to delete this record')");
Alternatively,
if the link button in ItemTemplate of datagrid has OnclientClick event exposed (which is present in ASP.NET2.0 onwards), you can add something like:
OnClientClick = 'return confirm("Are you sure you want to delete this entry?");'
Refer:
MSDN: Adding Client-Side Confirmation when Deleting[
^]
Try!