Good question. The general rule is to listen to yourself saying the word as it comes naturally to you. If the ending sounds like "sez" then write s's. If the ending sounds like "ss" or "zz" then you don't.
E.g. "I am going to Shirley Jones's house for lunch." When you say it, it sounds like "Jonezez"
"The bass's strings are untuned" Sounds like "bases".
"Put out the dogs' food" Here, there are many dogs, but you still say "dogz".
"I am amazed on the bonus's effect on worker effeciency". You say "bonusez".
"We cannot support the bonuses' costs." You say "bonusez" not "bonusezez"
Boiling this down to guidelines, we have this:
1. If the word ends in an "s" in the singular, you can make a possessive by adding 's.
2. If the word ends in s because it is a plural (like dogs or bonuses in the examples) then you make a possessive by adding an apostrophe. There is no change in pronunciation.
An exception is the name Jesus which always forms a possessive as if it were plural, and is pronounced like that. "Jesus' beard was never cut."
s If it's the 'a' word referring to the posterior, the UK spelling ends in 'e'. The American word for it ends it with an s
A 13-letter word that starts with "s" and ends with "s" is "schoolteachers."
you would use -es when a word ends in a -ch like rich or glitch you use the ending -es
Scissors is an 8 letter word. It begins and ends with S.
One Jones: "Mr. Jones's car." More than one Jones: "The Joneses' house." The rule is that you use the apostrophe at the end only when the word ends in s because it is a plural, like Joneses. Otherwise you form the possessive with an apostrophe and an s whether or not the word ends in s. NEVER EVER use an apostrophe to form a plural.
One example of a long word that starts with "s" and ends with "r" is "supercomputer."
An eight letter word that starts with S and ends with T: satiristshortestsmallestsmarteststagnantstalwartstiffeststridentsubtract
Sandman (starts with S ends with N - 7 letter word)
6 letter word that ends in s and is a unit of measurement: ounces
th answer to a word that hbegines and ends with s and has 6 letters is 'sauces'
SMILER - There is a mile between the s and the r!
Are you sure it ends in S? I am thinking jail, but if it ends in S it could be mess, pens, cans.