Try this

using this plugin

   cordova plugin add phonegap-plugin-push --variable SENDER_ID="XXXXXXX"

after that adding this

in to ionicPlatform.ready

var push = PushNotification.init({
    "android": {
        "senderID": "SENDER-ID"
    },
    "ios": {"alert": "true", "badge": "true", "sound": "true"}, 
    "windows": {} 
});

push.on('registration', function(data) {
    console.log("registration event");
    //here is your registration id
    console.log(data.registrationId);
});

I may be very late in answering your question, your answer is as below

1. Update your ionic to latest version i,e v2 and above.
2. Then create a project and add this plugin

cordova plugin add phonegap-plugin-push --variable SENDER_ID="XXXXXXXXX

3. Next goto src/app/app.component.ts file and add this code after platform.ready().then(()

   var push = Push.init({
       android: {
         senderID: "XXXXXXXXX"
       },
       ios: {
         alert: "true",
         badge: true,
         sound: 'false'
       },
       windows: {}
     });
     push.on('registration', (data) => {
       console.log(data.registrationId);
       alert(data.registrationId.toString());              
     });
   

   push.on('notification', (data) => { console.log(data); alert("Hi, Am a push notification"); });

4. Perform all the certification part according to apple guidelines(if any problem please do comment).
5. Finally implement push notification server side either in java or php or ionic.io ! All the best...