for ($xml->{job_info}{queue_info}{'Queue-List'}('@')) {
    print $_->{job_list}{slots};
}

##</code><code>##

#!/usr/bin/env perl -l

use strict;
use warnings;

use XML::Smart;

my $qstat = <<'EOX';
<?xml version='1.0'?>
<job_info revision="1.11">
  <queue_info>
    <Queue-List>
      <name>long_zeta@zeta09.local</name>
      <qtype>BIP</qtype>
      <slots_used>1</slots_used>
      <slots_resv>0</slots_resv>
      <slots_total>8</slots_total>
      <arch>lx26-amd64</arch>
      <resource name="arch" type="hl">lx26-amd64</resource>
      <resource name="num_proc" type="hl">8</resource>
      <job_list state="running">
        <JB_job_number>642412</JB_job_number>
        <JAT_prio>5.00248</JAT_prio>
        <JAT_ntix>0.00002</JAT_ntix>
        <JB_name>U6s53097</JB_name>
        <JB_owner>npatel37</JB_owner>
        <JB_project>correlat</JB_project>
        <JB_department>defaultdepartment</JB_department>
        <state>r</state>
        <cpu_usage>224919.00000</cpu_usage>
        <mem_usage>15753.53518</mem_usage>
        <io_usage>0.32690</io_usage>
        <tickets>0</tickets>
        <JB_override_tickets>0</JB_override_tickets>
        <JB_jobshare>0</JB_jobshare>
        <otickets>0</otickets>
        <ftickets>0</ftickets>
        <stickets>0</stickets>
        <JAT_share>0.00002</JAT_share>
        <slots>1</slots>
      </job_list>
    </Queue-List>
  </queue_info>
</job_info>
EOX

my $xml  = XML::Smart->new($qstat);

for ($xml->{job_info}->{queue_info}->{'Queue-List'}('@')) {
    print $_->{job_list}->{slots};
}

#for ($xml->{job_info}{queue_info}{'Queue-List'}('@')) {
#    print $_->{job_list}{slots};
#}