If tag1 and tag3 are equal, this is overly complicated.
This line:

conferences     NN      conference
[download]

might be wrong?

#!/usr/bin/perl
use strict;
use warnings;
     
use Data::Dumper qw(Dumper);

my %hash;

while (my $line = <DATA>)
{
    next if $line =~ /^\s*$/; # skip blank lines
    
    my ($tag1, $tag2, $tag3) = split(/\s+/, $line);
    next unless $tag2 eq 'NN';
    
    $hash{$tag3}++;
}

print Dumper \%hash;

=prints
$VAR1 = {
          'well' => 1,
          'conference' => 3,
          'International' => 1,
          'preparation' => 2
        };
=cut



__DATA__
The     DT      the
International   NN      International
for     IN      for
well    NN      well
preparation     NN      preparation
preparation     NN      preparation
in      IN      in
conference      NN      conference
conference      NN      conference
conferences     NN      conference
good    VVG     good
[download]