From the pbsnodes man page:

       -l             List  node  names  and  their  state.  If no state is
specified, only nodes in the DOWN, OFFLINE, or UNKNOWN states are
                      listed.  Specifying a state string acts as an output
filter.   Valid  state  strings  are  "free",  "offline",  "down",
                      "reserve", "job-exclusive", "job-sharing", "busy",
"time-shared", or "state-unknown".

But:

[root@hamming2 log]# pbsnodes -l reserve
pbsnodes: Unknown node  MSG=cannot locate specified node
[root@hamming2 log]# pbsnodes -l state-unknown
pbsnodes: Unknown node  MSG=cannot locate specified node
[root@hamming2 log]# pbsnodes -l job-exclusive
pbsnodes: Unknown node  MSG=cannot locate specified node
[root@hamming2 log]# pbsnodes -l job-sharing
pbsnodes: Unknown node  MSG=cannot locate specified node
[root@hamming2 log]# pbsnodes -l time-shared
pbsnodes: Unknown node  MSG=cannot locate specified node

Seems to work for "free",  "offline",  "down", "busy"

I also see why, from pbsnodes.c:

const char *NState[] =
  {
  "NONE",
  "active",
  "all",
  "busy",
  "down",
  "free",
  "offline",
  "unknown",
  "up",
  NULL
  };

Maybe add the missing or update man page?