When you uses an Edit control like a TMemo or TEdit component a context menu pops up with options to undo, copy, paste, select all, etc.

Unfortunally the TSynEdit component doesn’t include a menu like this, so you must write you own. You can fix this in a few lines of code using a interposer class. Check this unit which implements a standard context menu for a TSynEdit component, based on a TActionList (only be sure to include the uSynEditPopupEdit unit after of the SynEdit unit in your uses list).

unit uSynEditPopupEdit;

interface

uses
 ActnList,
 Menus,
 Classes,
 SynEdit;

type
  TSynEdit = class(SynEdit.TSynEdit)
  private
    FActnList: TActionList;
    FPopupMenu : TPopupMenu;
    procedure CreateActns;
    procedure FillPopupMenu(APopupMenu : TPopupMenu);
    procedure CutExecute(Sender: TObject);
    procedure CutUpdate(Sender: TObject);
    procedure CopyExecute(Sender: TObject);
    procedure CopyUpdate(Sender: TObject);
    procedure PasteExecute(Sender: TObject);
    procedure PasteUpdate(Sender: TObject);
    procedure DeleteExecute(Sender: TObject);
    procedure DeleteUpdate(Sender: TObject);
    procedure SelectAllExecute(Sender: TObject);
    procedure SelectAllUpdate(Sender: TObject);
    procedure RedoExecute(Sender: TObject);
    procedure RedoUpdate(Sender: TObject);
    procedure UndoExecute(Sender: TObject);
    procedure UndoUpdate(Sender: TObject);
    procedure SetPopupMenu_(const Value: TPopupMenu);
    function  GetPopupMenu_: TPopupMenu;
  public
    constructor Create(AOwner: TComponent); override;
    destructor Destroy; override;
  published
    property PopupMenu: TPopupMenu read GetPopupMenu_ write SetPopupMenu_;
  end;

implementation

uses
 SysUtils;

const
 MenuName='uSynEditPopupMenu';

procedure TSynEdit.CopyExecute(Sender: TObject);
begin
  Self.CopyToClipboard;
end;

procedure TSynEdit.CopyUpdate(Sender: TObject);
begin
  TAction(Sender).Enabled :=Self.SelAvail;
end;

procedure TSynEdit.CutExecute(Sender: TObject);
begin
  Self.CutToClipboard;
end;

procedure TSynEdit.CutUpdate(Sender: TObject);
begin
  TAction(Sender).Enabled :=Self.SelAvail and not Self.ReadOnly;
end;

procedure TSynEdit.DeleteExecute(Sender: TObject);
begin
  Self.SelText := '';
end;

procedure TSynEdit.DeleteUpdate(Sender: TObject);
begin
  TAction(Sender).Enabled :=Self.SelAvail and not Self.ReadOnly;
end;

procedure TSynEdit.PasteExecute(Sender: TObject);
begin
 Self.PasteFromClipboard;
end;

procedure TSynEdit.PasteUpdate(Sender: TObject);
begin
 TAction(Sender).Enabled :=Self.CanPaste;
end;

procedure TSynEdit.RedoExecute(Sender: TObject);
begin
 Self.Redo;
end;

procedure TSynEdit.RedoUpdate(Sender: TObject);
begin
 TAction(Sender).Enabled :=Self.CanRedo;
end;

procedure TSynEdit.SelectAllExecute(Sender: TObject);
begin
 Self.SelectAll;
end;

procedure TSynEdit.SelectAllUpdate(Sender: TObject);
begin
 TAction(Sender).Enabled :=Self.Lines.Text<>'';
end;

procedure TSynEdit.UndoExecute(Sender: TObject);
begin
 Self.Undo;
end;

procedure TSynEdit.UndoUpdate(Sender: TObject);
begin
 TAction(Sender).Enabled :=Self.CanUndo;
end;

constructor TSynEdit.Create(AOwner: TComponent);
begin
  inherited;
  FActnList:=TActionList.Create(Self);
  FPopupMenu:=TPopupMenu.Create(Self);
  FPopupMenu.Name:=MenuName;
  CreateActns;
  FillPopupMenu(FPopupMenu);
  PopupMenu:=FPopupMenu;
end;

procedure TSynEdit.CreateActns;

 procedure AddActItem(const AText:string;AShortCut : TShortCut;AEnabled:Boolean;OnExecute,OnUpdate:TNotifyEvent);
 Var
    ActionItem  : TAction;
  begin
    ActionItem:=TAction.Create(FActnList);
    ActionItem.ActionList:=FActnList;
    ActionItem.Caption:=AText;
    ActionItem.ShortCut:=AShortCut;
    ActionItem.Enabled :=AEnabled;
    ActionItem.OnExecute :=OnExecute;
    ActionItem.OnUpdate  :=OnUpdate;
  end;

begin
  AddActItem('&Undo',Menus.ShortCut(Word('Z'), [ssCtrl]),False,UndoExecute, UndoUpdate);
  AddActItem('&Redo',Menus.ShortCut(Word('Z'), [ssCtrl,ssShift]),False,RedoExecute, RedoUpdate);
  AddActItem('-',0,False,nil,nil);
  AddActItem('Cu&t',Menus.ShortCut(Word('X'), [ssCtrl]),False,CutExecute, CutUpdate);
  AddActItem('&Copy',Menus.ShortCut(Word('C'), [ssCtrl]),False,CopyExecute, CopyUpdate);
  AddActItem('&Paste',Menus.ShortCut(Word('V'), [ssCtrl]),False,PasteExecute, PasteUpdate);
  AddActItem('De&lete',0,False,DeleteExecute, DeleteUpdate);
  AddActItem('-',0,False,nil,nil);
  AddActItem('Select &All',Menus.ShortCut(Word('A'), [ssCtrl]),False,SelectAllExecute, SelectAllUpdate);
end;

procedure TSynEdit.SetPopupMenu_(const Value: TPopupMenu);
Var
  MenuItem : TMenuItem;
begin
  SynEdit.TSynEdit(Self).PopupMenu:=Value;
  if CompareText(MenuName,Value.Name)<>0 then
  begin
   MenuItem:=TMenuItem.Create(Value);
   MenuItem.Caption:='-';
   Value.Items.Add(MenuItem);
   FillPopupMenu(Value);
  end;
end;

function TSynEdit.GetPopupMenu_: TPopupMenu;
begin
  Result:=SynEdit.TSynEdit(Self).PopupMenu;
end;

destructor TSynEdit.Destroy;
begin
  FPopupMenu.Free;
  FActnList.Free;
  inherited;
end;

procedure TSynEdit.FillPopupMenu(APopupMenu : TPopupMenu);
var
  i        : integer;
  MenuItem : TMenuItem;
begin
  if Assigned(FActnList) then
  for i := 0 to FActnList.ActionCount-1 do
  begin
    MenuItem:=TMenuItem.Create(APopupMenu);
    MenuItem.Action  :=FActnList.Actions[i];
    APopupMenu.Items.Add(MenuItem);
  end;
end;

end.

And this is the final result.