It is declined:
N.que,who, which, what
G.de que,of whom
D.á que,to whom
Acc.que,whom
Abl.de que,from whom.

c) Quem, is only used of persons.

Singular and Plural.
N.quem,who
G.de quem,of whom
D.á quem,to whom
Acc.quem,whom
Abl.de quem,from whom.

d) Cujo, cuja, whose.

Singular.
Masculine.Feminine.
N.
G.de cujo,of whose de cuja
D.a cujo,to whosea cuja
Acc.cujo,whosecuja
Abl.de cujo,whose.de cuja.

Examples.

48.

7. Interrogative Pronouns.

Quem, qual, que, who, which, what?