Different stylebooks say different things on this matter. The way it's usually written is "Jones's book". However, some people prefer it to be "Jones' book", which is also entirely allowed. I usually leave it up to the person whose name it is. I know a guy named Gaines who prefers Gaines's, and a guy named Charles who prefers Charles'.
The possessive apostrophe in "Jones' book" goes after the 's' at the end of "Jones" because "Jones" is a proper noun ending in 's.' This is the accepted convention for indicating possession in this specific case.
Mrs Debase. (no apostrophe) Mrs Debase's handbag. (Possessive apostrophe)
Firm's. Any singular possessive where the word does not end in 's' is apostrophe 's' ('s).
"Companies" is the plural "company" and doesn't require an apostrophe unless you are using a plural possessive. With the plural possessive, the apostrophe should appear at the end of the word after the 's'.
The possessive is the standard form - playmate's - and the possessive of the plural can use only the apostrophe - playmates' - in accordance with standard usage.
daughter's wedding
visitors---If you are using visitors as a plural of visitor, then you don't need an apostrophe.Visitor's (note apostrophe s) is a singular possessive. That is my visitor's luggage.Visitors' (note s apostrophe) is a plural possessive. This is the visitors' lounge.
The plural of governor is governors (no apostrophe necessary). The plural possessive form of governor is governors'.
The possessive form of "kid" is "kid's," so the apostrophe goes before the s. For example, "the kid's toy."
If janitors is simply a plural word, then it doesn't need an apostrophe. Janitor's is a singular possessive (Janitor's responsibilities). Janitors' is the plural possessive (Janitors' responsibilities).
You don't need an apostrophe in that sentence. Studentsis a plural word, not a possessive.
Parents'......the apostrophe goes at the end of Parents because it is Plural Possessive.
Theoretically it should go at the end The Jones' - However - Words ending in just an apostrophe and nothing else usually have it removed.