JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
    <li class="race"><span Caption="Other" data-originalName="A"><input type="checkbox" id="Chk1" onclick="Selection();" /><label for="Chk1">A</label>
    <li class="race"><span Caption="Other" data-originalName="B"><input type="checkbox" id="Chk2" onclick="Selection();"/><label for="Chk2">B</label>
    <li class="race"><span Caption="Other" data-originalName="C"><input type="checkbox" id="Chk3" onclick="Selection();"/><label for="Chk3">C</label>
    <li class="race"><span Caption="Other" data-originalName="D"><input type="checkbox" id="Chk4" onclick="Selection();"/><label for="Chk4">D</label>
    <li class="race"><span Caption="Other" data-originalName="Unknown"><input type="checkbox" id="Chk5" onclick="Selection();"/><label for="Chk5">Unknown</label>
</ul>

JavaScript

$('.race').find('input:checkbox').filter(function(){
    return $(this).closest('span').attr('data-originalName') != 'Unknown';
}).prop('checked', true);