my $daten_ref; # neu
while (my @row = $sth_suchen->fetchrow_array()) {
...
# Am Ende der while-Schleife dann
$daten_ref->{ $hash{identnr} }->{ $hash{docname} } = { %hash };
} # Ende der while-Schleife

foreach my $identnr ( keys %$daten_ref ) {
    doc_vorhanden( $identnr, keys %{ $daten_ref->{$identnr} } );
}

sub doc_vorhanden {
    my ( $identnr, @docnames ) = @_;

...

    foreach my $docname ( @docnames )
    {
        my ( $doctyp, $head_de ) = @{ $daten_ref->{$identnr}->{$docname}->{ qw( doctyp head_de ) } }

        # hier die Ausgabe dazu
    }

 print '<table border="1" rules="groups">
                <colgroup>
                   <col width="50">
                   <col width="80">
                   <col width="300">
                   <col width="50">
                </colgroup>
                <thead>
                <tr>
                   <th>doc_typ</th>
                   <th>doc_name</th>
                   <th>headline</th>
                </tr></thead>
                <tbody>';
        foreach my $docname (@docnames)
        {
        my ($doctyp, $head_de)= @ {$daten_ref -> {$identnr}->{$docname}-> {qw(doctyp head_de) } };                    ##Zeile 344
        print '<tr>';
        print '    <td>'.$doctyp.'</td>
                   <td>'.$docname.'</td>
                   <td>'.$head_de.'</td>
                   <td><input type="button" value="Auswahl" onClick=""></td>
                </tr>';}
        print '</tbody></table>';
        print '<p><p><input type="button" value="Zur&uuml;ck" onClick="history.back()">';
        print "</form>

foreach my $identnr ( keys %$daten_ref ) {
    doc_vorhanden( $identnr, keys %{ $daten_ref->{$identnr} } );
}

foreach my $identnr ( keys %$daten_ref ) {
    doc_vorhanden( $identnr, $daten_ref, keys %{ $daten_ref->{$identnr} } );
}

sub doc_vorhanden {
    my ( $identnr, $daten_ref, @docnames ) = @_;

...