The possessive pronoun โ€œoneโ€™sโ€ requires an apostrophe before theย S, unlike โ€œits,โ€ โ€œhers,โ€ and other personal pronouns. Examples: โ€œpull oneself up by oneโ€™s own bootstraps,โ€ โ€œa jury of oneโ€™s peers,โ€ โ€œminding oneโ€™s own business.โ€

A simple test: try inserting โ€œanyoneโ€™sโ€ in place of โ€œoneโ€™s.โ€ If it works grammatically, you need the apostrophe in โ€œoneโ€™sโ€ too. When โ€œoneโ€™sโ€ is a contraction of โ€œone isโ€ it also requires an apostrophe: โ€œno oneโ€™s listening,โ€ โ€œthis oneโ€™s for you.โ€

The only times โ€œonesโ€ has no apostrophe are when it is being used to mean โ€œexamplesโ€ or โ€œpeopleโ€ as in โ€œripe onesโ€ or โ€œloved ones,โ€ or in the informal arithmetical expression โ€œthe ones column.โ€ย  ”