Where does the apostrophe go in a word with the s on the end?

IF the word is POSSESSIVE, it gets an 's.

Fred's cat was named Tigger. (The cat belongs to Fred, so Fred gets an 's).

Fred had a cat named Tigger. (The cat belongs to Fred and we told the reader this (HAD), and so we need not use an 's to designate Fred possessing the cat).

The United Nation's Geopolitical Organization, WHO, governs aspects of food commodities.

Note, possession can belong to a government entity, not just a single person.

The United States Army's Regional Warfare College is in Maryland.

Whereas...

The United States Armies are spread all over the world. Note that Armies are not specific as to which army we are talking about...could be the 20th Army Group, etc. But if we specify which army group it is, then it becomes possessive:

The United States Army's 20th Army Division is located in Montana.

Whenever in doubt, ask yourself, is this possessive? Does something here belong to someone or something? If so, it has an 's.

If you're talking about something that belonged to Charles Dickens, then the apostrophe come after the S because the S was already there. So you talk about having read Dickens' book. Same with Jesus, you follow Jesus' advice. If there wasn't an s already there, you'd add an s, and put the apostrophe before it, so you liked Jesus' advice better than Mohammed's advice, or you read Dickens' book before you read Hemingway's book.

A semi-colon is used where a sentence has two complete distinct sentences, each with its own subject and predicate. It could be two separate sentences. Like: My dog doesn't eat chocolate; he is a diabetic. Or: You spell Dickens with the apostrophe after the s; this is a general rule of spelling.