The Editor's Manual
Free learning resource on English grammar, punctuation, usage, and style.
“Who’s” is the contraction of “who is” or “who has,” while “whose” is the possessive form of “who.”
Form the possessive of a name ending in “s” by adding either an apostrophe and another “s” or just an apostrophe. The possessive of a plural name takes an apostrophe after the final “s.”