<?php
$html = <<<HTML
<body>
<tr>
<td class="highlightable group">НЕ ПОДХОДИТ</td>
<td class="pnum highlightable">НОМЕР</td>
<td class="highlightable onepair"><p class="pname">ПРЕДМЕТ</p><p class="pteacher">ИМЯ<span class="pcab"></span></p></td>
<td class="highlightable onepair"><p class="pname">ПРЕДМЕТ 2</p><p class="pteacher">ИМЯ 2<span class="pcab">НОМЕР 2</span></p></td>
</tr>
<tr>
<td class="highlightable group">НЕ ПОДХОДИТ</td>
<td class="pnum highlightable">НОМЕР</td>
<td class="highlightable onepair"><p class="pname">ПРЕДМЕТ</p><p class="pteacher">ИМЯ<span class="pcab"></span></p></td>
<td class="highlightable onepair"><p class="pname">ПРЕДМЕТ 2</p><p class="pteacher">ИМЯ 2<span class="pcab">НОМЕР 2</span></p></td>
</tr>
<tr>
<td class="highlightable group">ПОДХОДИТ</td>
<td class="pnum highlightable">НОМЕР</td>
<td class="highlightable onepair"><p class="pname">ПРЕДМЕТ</p><p class="pteacher">ИМЯ<span class="pcab"></span></p></td>
<td class="highlightable onepair"><p class="pname">ПРЕДМЕТ 2</p><p class="pteacher">ИМЯ 2<span class="pcab">НОМЕР 2</span></p></td>
</tr>
<tr>
<td class="highlightable group">НЕ ПОДХОДИТ</td>
<td class="pnum highlightable">НОМЕР</td>
<td class="highlightable onepair"><p class="pname">ПРЕДМЕТ</p><p class="pteacher">ИМЯ<span class="pcab"></span></p></td>
<td class="highlightable onepair"><p class="pname">ПРЕДМЕТ 2</p><p class="pteacher">ИМЯ 2<span class="pcab">НОМЕР 2</span></p></td>
</tr>
<tr>
<td class="highlightable group">ПОДХОДИТ</td>
<td class="pnum highlightable">НОМЕР</td>
<td class="highlightable onepair"><p class="pname">ПРЕДМЕТ</p><p class="pteacher">ИМЯ<span class="pcab"></span></p></td>
<td class="highlightable onepair"><p class="pname">ПРЕДМЕТ 2</p><p class="pteacher">ИМЯ 2<span class="pcab">НОМЕР 2</span></p></td>
</tr>
<tr>
<td class="highlightable group">НЕ ПОДХОДИТ</td>
<td class="pnum highlightable">НОМЕР</td>
<td class="highlightable onepair"><p class="pname">ПРЕДМЕТ</p><p class="pteacher">ИМЯ<span class="pcab"></span></p></td>
<td class="highlightable onepair"><p class="pname">ПРЕДМЕТ 2</p><p class="pteacher">ИМЯ 2<span class="pcab">НОМЕР 2</span></p></td>
</tr>
</body>
HTML;
$dom = new DOMDocument;
$dom->loadXML($html);
$content = '';
$xpath = new DOMXPath($dom);
foreach ($xpath->query('//td[.="ПОДХОДИТ"]/..') as $row) {
$content .= $dom->saveXML($row) . PHP_EOL;
}
echo $content;