<section class="list">
<div class="nav">
<button class="btn-add">
<span>add</span>
</button>
</div>
</section>
<section class="users">
<div class="nav">
<button class="btn-add">
<span>add</span>
</button>
</div>
</section>
$('button').click(function(e) {
console.log(this.closest('section').className);
});