Question

//Sort User Table
private void SortGridView(string sortExpression, string direction)
{
    DataTable dataTable = BindGridView(Session["useremail"].ToString()).Tables[0];
    if (dataTable != null)
    {
        DataView dataView = new DataView(dataTable);
        dataView.Sort = sortExpression + direction;

        UserTable.DataSource = dataView;
        UserTable.DataBind();
    }
}

protected void gridView_Sorting(object sender, GridViewSortEventArgs e)
{
    string sortExpression = e.SortExpression;
    if (GridViewSortDirection == SortDirection.Ascending)
    {
        GridViewSortDirection = SortDirection.Descending;
        SortGridView(sortExpression, " ASC");
    }

    else
    {
        GridViewSortDirection = SortDirection.Ascending;
        SortGridView(sortExpression, " DESC");
    }
}

public SortDirection GridViewSortDirection
{
    get
    {
        if (ViewState["sortDirection"] == null)
            ViewState["sortDirection"] = SortDirection.Ascending;
        return (SortDirection)ViewState["sortDirection"];
    }
    set { ViewState["sortDirection"] = value; }
}

When I Edit a user and update the edit or do some search, and clear the search the page loads and the sort is lost,

private DataSet BindGridView(string email)
    {
        .......
    }

 protected void btnUpdate_Click(object sender, EventArgs e)
   {
      .....
       BindGridView(Session["useremail"].ToString());
    }

everytime the page loads or some postback is done the sort is lost how to retain the sort.

Page load

 if (PermissionList.Any(item => item.Equals("Edit user")))        
     {            
            if (!IsPostBack)
            {
                BindGridView(Session["useremail"].ToString());
            }
        }

Answer 1

Whenever you perform a new sort on your gridview, store the sort expression in a hidden label, or field, and anytime you re-load/bind your gridview, use your saved sort expression to re-sort the table.

.aspx

<asp:Label id="lblHidSortExp" runat="server" visible="false"></asp:Label>

.aspx.cs

protected void gridView_Sorting(object sender, GridViewSortEventArgs e)
{
    string sortExpression = lblHidSortExp.Text;
    if(sortExpression == e.SortExpression)
        sortExpression += " DESC";
    else
        sortExpression == e.SortExpression;

   //not sure if this is exactly how you get your datatable, but you get the idea
   DataView myView = new DataView(BindGridView(Session["useremail"].ToString()).Tables[0]);
   myView.Sort = sortExpression;
   marksGridView.DataSource = myView;
   marksGridView.DataBind();

   //save sort state
   lblHidSortExp.Text = sortExpression;
}

So say in your update function, use your saved sort exp

protected void btnUpdate_Click(object sender, EventArgs e)
{
  .....//do update in db
   //reload your table in dataview
   DataView myView = new DataView(/*load table*/);
   //do sort
   myView.Sort = lblHidSortExp.Text;
   //bind gridview
   marksGridView.DataSource = myView;
   marksGridView.DataBind();
}