how get DataKeyNames of current rows in gridview in code behind

Set the DataKeyField in GridView as

<asp:gridview id="gvList" runat="server" datakeynames="Id" xmlns:asp="#unknown">
...........
</asp:gridview>

Then you can get the key value for each column as:

for (int i = 0; i < gvList.Rows.Count; i++)
    {
        Int32 key = Convert.ToInt32(gvList.DataKeys[i].Value.ToString());
    }

Or, if you are working between any cell-event you can use the object of DataGridViewCellEventArgs as

Int32 key = Convert.ToInt32(gvList.DataKeys[e.RowIndex].Value);