A notch apple is a golden apple that has the glow of an enchanted item. You don't need to enchant a regular golden apple, however. Instead, you need to craft it using an apple and 8 gold blocks. A gold block is made from 9 gold ingots, so 8 gold blocks are made from 72 gold ingots. Once crafted, you simply need to eat it.
You can also rarely find them in chests around the world. In one of my Xbox One Edition worlds, I found one in a woodland mansion. I'm not sure if they are exclusive to those or if you can find them in other structures as well.
Edit: If you are having trouble crafting it, you may have to do it manually as opposed to using the recipe book.
Edit: Notch apples can no longer be crafted. You have to find one in a chest in the world. The easiest way would be to find a seed that has a known Notch apple in a chest. I will update the guide if a seed has been posted in the comment section.