(Chicago Manual of Style)It is best, and, what is more, perfectly idiomatic, to use the double genitive when “one of So-and-so’s” is what you have in mind:
a student of his (that is, one of his students)
a student of Einstein’s (that is, one of Einstein’s students)
P.D. Pero es para personas, no para cosas. "He is a friend of John's" pero "He is a friend of the museum", "He is a friend of the family".Do we say "a friend of my uncle" or "a friend of my uncle's"? In spite of the fact that "a friend of my uncle's" seems to overwork the notion of possessiveness, that is usually what we say and write. The double possessive construction is sometimes called the "post-genitive" or "of followed by a possessive case or an absolute possessive pronoun" (from the Oxford English Dictionary, which likes to show off).