The author is Jonathan Kellerman. She likes
the author's books best. --->

The author whose books she likes best is
Jonathan Kellerman.

The sentence with whose has an adjective
clause: whose books she likes best. In the
clause, whose is the relative pronoun and is
used with books. The clause modifies the
subject of the sentence: the author.

________________________________

The people will be glad to help you.
The people's names are on this list. --->

The people whose names are on this
list will be glad to help you.

Here, the adjective clause is whose
names are on this list. The adjective
clause modifies the subject of the main
sentence: the people.

I enjoyed discussing the author. We had
just read the author's latest book. --->

I enjoyed discussing the author whose
latest book we had just rea d.

Again, the sentence with whose has an
adjective clause: whose latest book we
had just read. The clause modifies the
object of the main sentence: the author.

________________________________

I've contacted all the people. The people's
names are on this list. --->

I've contacted all the people whose names
are on this list.

Here, the adjective clause is whose names
are on this list. The clause modifies the
object of the main sentence: the people.

Do not use a subject relative pronoun
and a "regular" possessive "pronoun in
an adjective clause:

wrong:
*The author who / that his books she
likes best is Jonathan Kellerman.

wrong:
*The people who / that their names are
on this list will be glad to help you.

wrong:
*I enjoyed discussing the author who / that
his latest book we had just read.

wrong:
*I've contacted all the people who / that
their names are on this list.

wrong:
*She just bought a computer that / which
its processor speed is 450 mhz.

Whose clauses for Things

There is a problem when you want to
make a possessive adjective clause for
things--because English does not have
a special relative pronoun for this situation:

She just bought a computer. The computer's
processor speed is 450 mhz. --->

She just bought a computer ??? processor
speed is 450 mhz.

___________________________________

Important: Because English does not
have a possessive relative pronoun that
refers to things, whose must be used:

She just bought a computer whose
processor speed is 450 mhz.

Bill has a car whose color is blue.

Sentences with adjective clauses like the
above are awkward because whose seems
more appropriate for people than for things.
You can avoid this problem by rephrasing
the adjective clause:

She just bought a computer which / that
has a processor speed of 450 mhz.

Bill has a blue car.