[جواد عوض]

The question is how to make the possessive of a singular word or name that ends in “s” or other sibilant [English (s), (z), (sh), (zh)]. Editors still disagree on the answer.

Both forms are correct. This is a question of style, not strictly of grammar. If you look at English newspapers, magazines and books today, you will see that they do not all agree on this. Newspapers tend to favor using only an apostrophe, while book publishers tend to favor using apostrophe + s.

The earlier convention was to omit the s. Later this evolved to omitting the s only in certain circumstances, which often depended on the pronunciation. This was often difficult to follow — was the possessive of Jones, for example, pronounced with one syllable or two? What should you do with names that end in silent s? Or what if you don’t know how a foreign name is pronounced and whether the final s is silent?

The current more popular rule is to add apostrophe + s to any singular possessive. This form does not depend on the pronunciation of the name or the resulting possessive, and is therefore never wrong.
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