In Phonics^x, Apostrophes^x

Mr Jones's briefcase or Mr Jones' briefcase?During my high school, I was taught to use the second one. Later, I learnt that both are acceptable. Source 1:Some writers will say that the -s after Charles' is not necessary and that adding only the apostrophe (Charles' car) will suffice to show...

1. Please tell me how can a person make the right decision when confronted those ajectives with a plural 's' ending? do phonics teaching obtained a first-class honors degree -- For this, I think it need (subjunctive OK since the context allude to the notion that this is sort of a recommendation...