What is the correct possessive spelling of Davis?

Answer 1

Depending on whom you ask, you form the possessive of a proper name ending in s either by adding 's (apostrophe + s) or by simply adding an apostrophe. It is more traditional to add 's, which would give you Davis's.

This is not to say that Davis', without the final s, is necessarily incorrect. If you read newspaper articles from the Associated Press, you'll find that they form possessives this way, just adding an apostrophe to the name, because that is what the AP's stylebook recommends. On the other hand, the Chicago Manual of Style opts for 's, but makes exceptions for a few specific names such as Jesus and Moses, and names of more than one syllable that end in an "eez" sound, such as Socrates, where the simple apostrophe is preferred.

Answer 2

The correct possessive spelling of "Davis" is "Davis'".