Printing Spool File

Assuming you are using windows (which seems valid),

you can use ReadPrinter to read the buffer of the printer. The declaration of ReadPrinter is as follows:

BOOL ReadPrinter(
  HANDLE hPrinter,      // handle to printer object
  LPVOID pBuf,          // data buffer
  DWORD cbBuf,          // size of data buffer
  LPDWORD pNoBytesRead  // bytes received
);

* Note however that this will only work if the printer is bidirectional, that is it allows it's buffer to be read.

But from the context of your question, i think you are just trying to know how many printing jobs are there.

This can be done using GetPrinter or EnumPrinters. If you only have one printer, you can use GetPrinter to get the number of print jobs else use EnumPrinters to get the print jobs of all the printers.The declaration of GetPrinter is:

BOOL GetPrinter(
  HANDLE hPrinter,    // handle to printer
  DWORD Level,        // information level
  LPBYTE pPrinter,    // printer information buffer
  DWORD cbBuf,        // size of buffer
  LPDWORD pcbNeeded   // bytes received or required
);

Put Level as 2. Get the handle to printer by calling OpenPrinter.
The declaration is as follows.

BOOL OpenPrinter(
  LPTSTR pPrinterName,         // printer or server name
  LPHANDLE phPrinter,          // printer or server handle
  LPPRINTER_DEFAULTS pDefault  // printer defaults
);

GetPrinter will return a PRINTER_INFO_2 structure in the buffer pointed to by pPrinter. The PRINTER_INFO_2 structure is as follows:

typedef struct _PRINTER_INFO_2 {
  LPTSTR    pServerName;
  LPTSTR    pPrinterName;
  LPTSTR    pShareName;
  LPTSTR    pPortName;
  LPTSTR    pDriverName;
  LPTSTR    pComment;
  LPTSTR    pLocation;
  LPDEVMODE pDevMode;
  LPTSTR    pSepFile;
  LPTSTR    pPrintProcessor;
  LPTSTR    pDatatype;
  LPTSTR    pParameters;
  PSECURITY_DESCRIPTOR pSecurityDescriptor;
  DWORD     Attributes;
  DWORD     Priority;
  DWORD     DefaultPriority;
  DWORD     StartTime;
  DWORD     UntilTime;
  DWORD     Status;
  DWORD     cJobs;
  DWORD     AveragePPM;
} PRINTER_INFO_2, *PPRINTER_INFO_2;

The value you want is cJobs.

It seems however that your printer works on a network, and many computers can request printing. I suppose there is a print server to handle all these requests. Therefore all the spooling will be done at a centralized location i.e. the print server. I believe all you have to do is use OpenPrinter on that printer and use the above steps.

If however you have more than one printer connected to the network, you will have to get all the jobs on all the printers and add them together to get the total number of jobs. It is good if you know all the names of the Printers on the network, then you can repeat the steps for all the printers.

It is however worthwhile to consider using EnumPrinters instead.
The declaration of EnumPrinters is as follows:

BOOL EnumPrinters(
  DWORD Flags,         // printer object types
  LPTSTR Name,         // name of printer object
  DWORD Level,         // information level
  LPBYTE pPrinterEnum, // printer information buffer
  DWORD cbBuf,         // size of printer information buffer
  LPDWORD pcbNeeded,   // bytes received or required
  LPDWORD pcReturned   // number of printers enumerated
);

Again put Level as 2. Put Flags as PRINTER_ENUM_LOCAL, Name as NULL. First call EnumPrinters with cbBuf = 0. The function will fail, but pcbNeeded will point to the size of the buffer needed (that is the value cbBuf has to take). Then call EnumPrinters again with the correct cbBuf value. It will return an array of  PRINTER_INFO_2 structures pointed to by pPrinterEnum. Yes, you want the cJobs in the structures.