#!/usr/bin/env perl -l

use strict;
use warnings;

my %call_subs = ( "PN" => "English, Film, Theater", );

# Your line gives "Global symbol "$call" requires explicit package name ...":
#my @subjects = split(/, /, $call_subs{$call});

# This works:
my @subjects = split(/, /, $call_subs{PN});

print for @subjects;