<!-- begin snippet: js hide: false console: true babel: false -->
<!-- language: lang-js -->
$(':checkbox').on('click',function() { if(this.checked) { console.log($(this).next('label').text()); } });
<!-- language: lang-html -->
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script> <div class="col-6 col-12-small"> <h4>Document Submited</h4> <input type="checkbox" id="idcopy" name="checkbox"> <label for="idcopy">NIC Copy</label> <input type="checkbox" id="birthcertificate" name="checkbox"> <label for="birthcertificate">Birth Certificate</label> <input type="checkbox" id="nomineeNic" name="checkbox"> <label for="nomineeNic">Nominee NIC copy</label> <input type="checkbox" id="agreement" name="checkbox"> <label for="agreement">Agreement</label> </div>
<!-- end snippet -->

You call get all element attribute by `attr(name)` ....
<!-- begin snippet: js hide: false console: true babel: false -->
<!-- language: lang-js -->
$(':checkbox').on('click',function() { if(this.checked) { console.log($(this).next('label').attr('for')); } });
<!-- language: lang-html -->
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script> <div class="col-6 col-12-small"> <h4>Document Submited</h4> <input type="checkbox" id="idcopy" name="checkbox"> <label for="idcopy">NIC Copy</label> <input type="checkbox" id="birthcertificate" name="checkbox"> <label for="birthcertificate">Birth Certificate</label> <input type="checkbox" id="nomineeNic" name="checkbox"> <label for="nomineeNic">Nominee NIC copy</label> <input type="checkbox" id="agreement" name="checkbox"> <label for="agreement">Agreement</label> </div>
<!-- end snippet -->