зачем создавать отдельные для каждой опции?
почему бы не генерировать only?
var objJSON = ['industry one', 'second industry', 'third ...']; //JSON.parse(response['data'][0].certificate);
setTimeout(function(){ // timeout for DEMO only
$('#DepartmentsDropDownList').empty();
//if(isOptional || notRequiredInput)
// $('#DepartmentsDropDownList').append('<option value=""> -- Select an item</option>');
for(var i in objJSON) {
$('#DepartmentsDropDownList').append('<option value="'+ objJSON[i] +'">'+ objJSON[i] +'</option>');
}
}, 1000);
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div id="input_container">
<select id="DepartmentsDropDownList" class="form-control" name="department[]">
<option> -- Loading items...</option>
</select>
</div>
Если вы хотите отдельно выбрать для каждого элемента
var objJSON = ['industry one', 'second industry', 'third ...']; //JSON.parse(response['data'][0].certificate);
setTimeout(function(){ // timeout for DEMO only
$('#inputs_container').empty();
//if(isOptional || notRequiredInput)
// $('#DepartmentsDropDownList').append('<option value=""> -- Select an item</option>');
for(var i in objJSON) {
$('#inputs_container').append('<div> <select><option value="'+ objJSON[i] +'">'+ objJSON[i] +'</option></select> </div>');
}
}, 1000);
<div id="inputs_container"></div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
Выбранные сертификаты Решение
var objJSON = ['certification one', 'certification two', 'certification five']; //JSON.parse(response['data'][0].certificate);
$('#DepartmentsDropDownList').val(objJSON);
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div id="input_container">
<select id="DepartmentsDropDownList" class="form-control" name="department[]" multiple="multiple" style="height: 100px;">
<option value="certification one">certification one</option>
<option value="certification two">certification two</option>
<option value="certification three">certification three</option>
<option value="certification four">certification four</option>
<option value="certification five">certification five</option>
</select>
</div>