Where can I wash my hands?

...wa doko desuka? : Where is ....?

toire : W.C., restroom
doko : where
-wa : (attached after the subject word)
desu : is,are
-ka : (attached at the end of the interrogative sentense)

Toire wa doko desuka ? : restroom, where, is ; Where is the restroom?

denwa : telephone

Denwa wa doko desuka ? : telephone, where, is : Where is a telephone? Where can I make a telephone call?

... wa doko ni arimasuka ? : (same with "...wa doko desuka ?") Where is .....?

Toire wa doko ni arimasuka ? : Where is a restroom?
Denwa wa doko ni arimasuka? : Where is a telephone?