Watching YouTube App from your iOS Devices (iphone, ipad, ipod, etc) on your smart TV is a breeze to do. You can pair it by pushing the pairing icon on your youtube app (make sure you have updated version) or you can do it manually by getting a code from your smart TV and entering it into your connected TV settings option from your YouTube app.
Please note that a smart TV is a TV which basically has integrated Internet connectivity as well as pre-installed apps. I am using a Samsung Smart 4K TV as in the below links. Let me know if you have any questions.
———Samsung 4k Smart TV————-