Japanese has a few different dialectic variants but basically uses two different types of writing known as Hiragana and Katakana.
In Hirabgana 'John' looks like this: ジョン
In Katakana 'John' looks like this: じょん
If you want to look up another name in Japanese, a good website to use is Kanjizone, which has a great name translator system. You can find that here:
You can also work out your own name through using the chart of phonetics pictured above. Japanese translations of names can be learnt through learning the different stresses of words to find the letters attached.
I've attached a video below that might help to show you how the written language was formed and how, by learning a few essential basics, you will soon be able work out more complex words for yourself: