How do I add a new printer connection to a remote computer?

Use the Win32_Printer class and the AddPrinterConnection method.

var
  FSWbemLocator : OLEVariant;
  FWMIService   : OLEVariant;
  FWbemObject   : OLEVariant;
begin;
  FSWbemLocator := CreateOleObject('WbemScripting.SWbemLocator');
  FWMIService   := FSWbemLocator.ConnectServer('localhost', 'root\CIMV2', '', '');
  FWbemObject   := FWMIService.Get('Win32_Printer');
  FWbemObject.AddPrinterConnection('\\PrintServer1\ArtDepartmentPrinter');
end;

How do I set the default printer?

Use the Win32_Printer class and the SetDefaultPrinter method.

const
  wbemFlagForwardOnly = $00000020;
var
  FSWbemLocator : OLEVariant;
  FWMIService   : OLEVariant;
  FWbemObjectSet: OLEVariant;
  FWbemObject   : OLEVariant;
  oEnum         : IEnumvariant;
  iValue        : LongWord;
begin;
  FSWbemLocator := CreateOleObject('WbemScripting.SWbemLocator');
  FWMIService   := FSWbemLocator.ConnectServer('localhost', 'root\CIMV2', '', '');
  FWbemObjectSet:= FWMIService.ExecQuery(Format('SELECT * FROM Win32_Printer Where Name = "%s"',['PrinterName']),'WQL',wbemFlagForwardOnly);
  oEnum         := IUnknown(FWbemObjectSet._NewEnum) as IEnumVariant;
  if oEnum.Next(1, FWbemObject, iValue) = 0 then
    FWbemObject.SetDefaultPrinter();
end;

How do I cancel print jobs using WMI?

Use the Win32_Printer class, and the CancelAllJobs method.

const
  wbemFlagForwardOnly = $00000020;
var
  FSWbemLocator : OLEVariant;
  FWMIService   : OLEVariant;
  FWbemObjectSet: OLEVariant;
  FWbemObject   : OLEVariant;
  oEnum         : IEnumvariant;
  iValue        : LongWord;
begin;
  FSWbemLocator := CreateOleObject('WbemScripting.SWbemLocator');
  FWMIService   := FSWbemLocator.ConnectServer('localhost', 'root\CIMV2', '', '');
  FWbemObjectSet:= FWMIService.ExecQuery('SELECT * FROM Win32_Printer','WQL',wbemFlagForwardOnly);
  oEnum         := IUnknown(FWbemObjectSet._NewEnum) as IEnumVariant;
  while oEnum.Next(1, FWbemObject, iValue) = 0 do
  begin
    FWbemObject.CancelAllJobs();
    FWbemObject:=Unassigned;
  end;
end;

How do I determine the default printer for a computer?

Use the Win32_Printer class, and check whether the Default property is True.

const
  wbemFlagForwardOnly = $00000020;
var
  FSWbemLocator : OLEVariant;
  FWMIService   : OLEVariant;
  FWbemObjectSet: OLEVariant;
  FWbemObject   : OLEVariant;
  oEnum         : IEnumvariant;
  iValue        : LongWord;
begin;
  FSWbemLocator := CreateOleObject('WbemScripting.SWbemLocator');
  FWMIService   := FSWbemLocator.ConnectServer('localhost', 'root\CIMV2', '', '');
  FWbemObjectSet:= FWMIService.ExecQuery('SELECT * FROM Win32_Printer Where Default = True','WQL',wbemFlagForwardOnly);
  oEnum         := IUnknown(FWbemObjectSet._NewEnum) as IEnumVariant;
  if oEnum.Next(1, FWbemObject, iValue) = 0 then
  begin
    Writeln(Format('Name    %s',[String(FWbemObject.Name)]));// String
    FWbemObject:=Unassigned;
  end;
end;

This post is based in the MSDN entry WMI Tasks: Printers and Printing