(In my case, the phone rang at 1:30 a.m. and I couldn't get back to sleep. Now what the hell are you doing up at this hour?)
There are a few exceptions. When are there not in English? The possessive form of Jesus and Moses take an apostophe only:
For singular proper nouns ending in s, stylists differ. Some use a style similar to German and simply add an apostrophe (Camus' novel, King Charles' crown). This is allowed by the department and is undoubtedly easier for students to follow. However, the general convention in English--both in American and British usage--is to add an apostrophe and an s (King Charles's crown, Texas's weather, Marx's ideology). The MLA Handbook suggests doing this in all cases, whereas many style books make exceptions for the names Jesus and Moses, for polysyllabic Greek names ending in es, and for any instance where an apostrophe alone more accurately reflects pronunciation (Jesus' ministry, Moses' leadership, Aristophanes' plays, Camus' novel).
What's the rule on the possessive of acronyms ending in the letter "S" (like "IRS")? Should it be:
What is the IRS's position on this issue?
What is the IRS' position on this issue?
For singular proper nouns ending in s, stylists differ. Some use a style similar to German and simply add an apostrophe (Camus' novel, King Charles' crown).
Joe, Don't shoot the messenger. I'm only relating what's in the Chicago Manual of Style. I agree with you, btw.
It may offer you some comfort to know that even Germans have problems with the genitive. A common error made by native-speakers of German is to use an apostrophe - English-style - in possessive forms. For instance, they will often write "Karl's Buch" instead of the correct form, "Karls Buch." Some observers claim this is an influence of English, but it is an influence that is often seen on store signs and even on the sides of trucks in Austria and Germany.
Names add -s (no apostrophe!) in the genitive, regardless of gender or number; if the name already ends in an -s or -z, only an apostrophe is added. Martines Jacke, Hans' Handschuhe, Müllers Auto. Names of people precede the noun possessed, other names typically follow: die Zukunft Europas.
Source: German Case Forms Reference