Why JavaScript onClick doesn't trigger jQuery submit function?

make a function out of it and trigger it with onclick like this:

<input id="submitBtn" style="margin-top:20px;" type="button" onclick="myfunction()" value="Opdater">

function myfunction() {
var form = $(this);
        $.ajax({ 
             url   : form.attr('action'),
             type  : form.attr('method'),
             data  : form.serialize(), // data to be submitted
             success: function(response){
                $("#showFancyBoxThankYouLink").click();
             }
        });
    return false;
}

Is the javascript running after the form has been rendered? If not, either make sure that your javascript is after the form or try to have it run after the document has loaded.

$(document).ready(function() {
  $("#form94").submit(function() {
    var form = $(this);
        $.ajax({ 
             url   : form.attr('action'),
             type  : form.attr('method'),
             data  : form.serialize(), // data to be submitted
             success: function(response){
                $("#showFancyBoxThankYouLink").click();
             }
        });
    return false;
  });
});

Another way to go about having the form submit is to add the onsubmit attribute to your form and have it return a function. You could also change your button type to submit and remove the onclick attribute.

<form id="form94" name="form94" onsubmit="return SubmitMyForm();">
  <input type="submit" value="Opdater">
</form>

<script>
function SubmitMyForm() {
    var form = $(this);
    $.ajax({ 
         url   : form.attr('action'),
         type  : form.attr('method'),
         data  : form.serialize(), // data to be submitted
         success: function(response){
            $("#showFancyBoxThankYouLink").click();
         }
    });
    return false;
}
</script>

Without a code example, it is hard to tell. But also, some browsers only submit a form when a user clicks a submit button, you cannot submit via script.

There are also a ton of other SO posts around this topic and they all either boil down to the form not existing when the submit event is attached (is your script executing at the top of the document or on the document's ready event?).

Form doesn't exist yet: Why Jquery form submit event not firing? Jquery .Submit() is not triggering submit event

Submitting via script: Should jQuery's $(form).submit(); not trigger onSubmit within the form tag?

Not using a submit button: jQuery submit not firing

replace this

onclick="document.getElementById('form94').submit();"

with onclick="$( "#form94" ).submit();"

The javascript submit() is not bubbling in IE and they might be other gotchas.