What does the nightingale want?

Hint 1 of 15:

I'd suggest waiting until you figure out if the nightingale belongs to 
anyone.

Hint 2 of 15:

Have you talked to the jester in the pawn shop?

Hint 3 of 15:

He'll show up from time to time.  Talk to him to see what he has to say.

Hint 4 of 15:

Eventually, he will mention Cassima.  Find some way to introduce yourself.

Hint 5 of 15:

You've used it before as a means of identification.

Hint 6 of 15:

Show him your family ring.  You'll find out that the nightingale belongs to
Cassima.  Now you can use the bird as a messenger.

Hint 7 of 15:

The bird is probably very lonely.  Maybe you can find it a friend.

Hint 8 of 15:

There is a tin nightingale available in the pawn shop.  Play it for the
real one.

Hint 9 of 15:

Maybe you can send Cassima a message ... Look in the book shop.