HP Color LaserJet 5500 Technical Reference Manual page 119

Comments:
If your application has status readback capability, you can
request the default setting of any valid environment variable.
The returned value indicates the User Default Environment
value for the feature. Since the DINQUIRE command returns
only the value for one feature, you must send multiple
DINQUIRE commands for data about more than one feature.
If the printer does not support the variable, the response is:
@PJL DINQUIRE [LPARM: personality | IPARM: port ]
~ variable <CR><LF>
"?"<CR><LF>
<FF>
If a printer language-specific variable is not available
because that printer language is not installed or is invalid,
or if a port-specific variable is not available because that
port is not supported, the command will return an
appropriate error code if USTATUS DEVICE=VERBOSE is
enabled.
Note
The LPARM : personality option must be used when
requesting printer language-specific information.
The IPARM : port option must be used when requesting
port-specific information.
Status Readback Commands 7-11