What is the correct way to use 's when spelling a name ending in x?

Question

When writing a name such as Maddox---do you use 's or s'???

Answer 1

Maddox's

Answer 2

Agreed.  It's only "s-apostrophe" if the item is belonging to many Maddoxes.  But assuming that there is just one Maddox, then it's "Maddox's such-and-such."