on grid view row data bound you can add attribute
protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
{
e.Row.Attributes.Add("onmouseover", "ShowRowNumber(" + e.Row.RowIndex + ")");
}
}
java script function should be
function ShowRowNumber(number)
{
alert(number);
}
i hope it will work.