The following can be found inthe K2 Documentation. It will iterate through all available items for a user and return properties for that item:

 foreach (WorklistItem worklistItem in connection.OpenWorklist())

                {

                    // open the worklist item

                    connection.OpenWorklistItem(worklistItem.SerialNumber);

                    if (worklistItem != null)

                    {

                        // retrieve properties of worklist item

                        Console.WriteLine("Process Instance Name: " + worklistItem.ProcessInstance.Name);

                        Console.WriteLine("Process Destination: " + worklistItem.ActivityInstanceDestination.Name);

                        Console.WriteLine("Process Folio: " + worklistItem.ProcessInstance.Folio);

                    }

                 }

        Console.WriteLine("End of worklist items.");

        Console.ReadLine();

You could of course open a worklist item directly if you have its serial number already.