Is there a way to differentiate Kanji and Hanzi? eg 後樂園 is completely kanji but I thought it was a place in Taiwan until I looked it up and it was in Japan. Also what about reading it in the Chinese reading (hou le yuan) instead of the actual Japanese reading (korakuen)? I’m confused on cultural notes such as these
You can only differentiate Kanji and Hanzi by looking into the context. Most Japanese Kanji look exactly like Chinese Hanzi because they were copied from  Hanzi. 

There are few unique Kanji that's coined by Japanese and not in use in Chinese. Those are called Kokuji. Kokuji are inspired by Hanzi, but not copied from, they can be easily identified as Japanese

Also, some Japanese characters are simplified different from the Mainland China's simplied Hanzi, but the non-simplified Kanji all look the same as traditional Chinese