HTMLSelectElement.labels

var labelElements = select.labels;

<label id="label1" for="test">Label 1</label>
<select id="test">
  <option value="1">Option 1</option>
  <option value="2">Option 2</option>
</select>
<label id="label2" for="test">Label 2</label>

window.addEventListener("DOMContentLoaded", function() {
  const select = document.getElementById("test");
  for(var i = 0; i < select.labels.length; i++) {
    console.log(select.labels[i].textContent); // "Label 1" and "Label 2"
  }
});