Your question doesn't make sense to me. A JetDirect is a print server (an ethernet device that accepts print jobs from PC's and outputs the into a printer). If you're trying to get a raw print file (command file) of a print job intended for an HP printer, install the printer to LPT1, then change the 'port' to FILE:, and every time you print to that printer it should prompt you for a file name. The resulting file would generally be a PCL command file in the version needed by the printer you installed the driver for.
Is that what you're asking?