my %anchors = map { $_ => 1 } qw/ Na Ne Ni No Nu /;

while (my $line = <DATA>) {
    my ($number, $item) = split ' ', $line;

    my ($first_two) = $item =~ /^(..)/
        or die "Word too short: $line";

    if (delete $anchors{$first_two}) {
        print "Insert '$first_two' anchor here!\n";
    }

    print $line;
}

__DATA__
   1930:    Nails               <-- #Na here
   1939:    Navy
   1940:    Nazi
   1941:    Nearsighted         <-- #Ne here
   1942:    Neck
   1961:    Newspaper_Reporter
   1963:    Nickname            <-- #Ni here
   1964:    Niece
   1971:    Nipples  
   1972:    Nobility            <-- #No here
   1973:    Noise  
   1981:    November
   1982:    Nuclear_Bomb        <-- #Nu here
   1984:    Numbers

##</code><code>##

Insert 'Na' anchor here!
   1930:    Nails               <-- #Na here
   1939:    Navy
   1940:    Nazi
Insert 'Ne' anchor here!
   1941:    Nearsighted         <-- #Ne here
   1942:    Neck
   1961:    Newspaper_Reporter
Insert 'Ni' anchor here!
   1963:    Nickname            <-- #Ni here
   1964:    Niece
   1971:    Nipples
Insert 'No' anchor here!
   1972:    Nobility            <-- #No here
   1973:    Noise
   1981:    November
Insert 'Nu' anchor here!
   1982:    Nuclear_Bomb        <-- #Nu here
   1984:    Numbers