Do you write Max' or Max's?

Answer 1

You would write the latter, "Max's." It is generally accepted that to make a proper noun that ends in an "x' possessive, you need to add an "'s." The only exceptions are some French and other similar words with a silent "x" like "Bordeaux'" and "Vorreax'."

Answer 2

It depends on the style guide you are following. Some style guides recommend using "Max's" to show possession (e.g., Max's book), while others may suggest using "Max'" if the word already ends in s (e.g., Max' book).