Q:

onclick event inside bootstrap popover

When inbox button is clicked it runs inbox_open() function
and in inbox header 3 buttons appear but onclick event listener is missing.
Check code after // inbox.open comment, critical lines: b.onclick = function() { console.log("button was clicked"); } andinbox.setAttribute("title", poH.innerHTML);

// inbox
var inbox = document.getElementById("inbox");
var inbox_news = document.getElementById("inbox_news");

var poH = document.createElement("span");
var poC = document.createElement("span");

var new_from_to = [0, 2, 3];
var number_of_news = [2, 1, 2];
var news_price_data = [10, 20, 30, 40, 50];

// inbox.open
function inbox_open() {
  for (var i = 0; i < number_of_news.length; i++) {
    var b = document.createElement("button");
    b.innerHTML = (i + 1);
    b.className = "poH";
    b.onclick = function() {
      console.log("button clicked");
    }
    poH.appendChild(b);
  }
  inbox.setAttribute("title", poH.innerHTML);
}

// inbox.addEventListener
inbox.onclick = inbox_open();

// aloud BS 4 popover to run
$(document).ready(function() {
  $('[data-toggle="popover"]').popover();
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.0/umd/popper.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.1.0/js/bootstrap.min.js"></script>

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.1.0/css/bootstrap.min.css">

<!-- HTML -->
<button id="inbox" class="btn btn-primary btn-sm" style="float: right; margin: 30px 30px 0 0;" data-toggle="popover" data-placement="left" data-html="true" title="" data-content="">inbox <span id="inbox_news"></span></button>

A:

The problem is that the onclick function is not being bound to the buttons, simply because of the way Bootstrap's Popovers work.  You can add the following few lines to add the onclick listener when the buttons become visible:
$('#inbox').on('shown.bs.popover', function () {

    var btns = document.getElementsByClassName("poH");
    for (var i=0; i < btns.length; i++) {
        btns[i].onclick = function() { console.log("shit"); };
    }

});

Just add the above after your $(document).ready(...) line.

