JSFiddle - React, Tailwind, and code Playground

HTML

<b>Table:</b> <br>
<table id="yourTable">
    <tr><td>A1</td><td>A2</td><td>A3</td></tr>
    <tr><td>B1</td><td>B2</td><td>B3</td></tr>
    <tr><td>B1</td><td>C2</td><td>C3</td></tr>
</table>
<br>
    <b>Select:</b> <select id="yourSelect"></select>

JavaScript

function useNthColumn(n) {

   var data = [],
       i,
       yourSelect,
       unique;

   $("#yourTable tr td:nth-child("+n+")").each(function () {
        data.push($(this).text());           
   });

   // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter
   // Use this function if your table is not large as the time complexity is O(n^2)
   unique = data.filter(function(item, i, arr) {
       return i == arr.indexOf(item);
   });

   yourSelect = $('#yourSelect');
   for (i = 0; i < unique.length; i += 1) {
        yourSelect.append("<option>"+unique[i]+"</option>");
   }
}

useNthColumn(1);