SO:https://stackoverflow.com/questions/47787983/how-to-find-an-attribute-that-passed-in-to-a-component-did-changed-ember

components.some-setup-section.js

import Ember from 'ember';

export default Ember.Component.extend({
  processingOfIdObserver: Ember.observer('processingOfId', function(){console.log(this.get('processingOfId'));})
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  processingOfId: 'dd',
  
  actions: {
    	changeMe(){
        this.set('processingOfId', 'Hi');
      }
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
<br>
<button {{action "changeMe"}}>Change</button>
<br>
<br>
<br>
{{some-setup-section
      processingOfId=processingOfId
     }}

templates.components.some-setup-section.hbs

{{yield}}
processingOfId is :
{{processingOfId}} 

twiddle.json

{
  "version": "0.12.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.12.0",
    "ember-template-compiler": "2.12.0",
    "ember-testing": "2.12.0"
  },
  "addons": {
    "ember-data": "2.12.1"
  }
}