JSFiddle - React, Tailwind, and code Playground

HTML

<div class="dashboard_section_item template">
    <label for="add_listname_label">Assign to list</label>
    <br/>
    <select name="mod_list" class="mod_list">
        <option value="1">Option 1</option>
        <option value="2">Option 2</option>
        <option value="3">Option 3</option>
        <option value="4">Option 4</option>
    </select>
</div>

<button class="add-new">Add a new select</button>
<hr>

CSS

.template { display: none; }

JavaScript

$(".add-new").on("click", function () {
    var $newSelect = $(".template").clone().removeClass("template");
    $(this).next().after($newSelect);
});

$(document).ready(function () {
    $(document).on("change", ".mod_list", function () {
        // this is the select you changed the value
        var $changedValueSelect = $(this);
        // do stuff, ajax and so on
        console.log($changedValueSelect.val());
    });
});