1.what does the Jackdaw call the "Third Joke"?

 One bear objected to Bulldog’s opinion and it said animals won’t roll over like Uncle Andrew. At the same time, it rose to his hind legs and took a step backwards, tripped over a low branch and fell flat on his back. Jackdaw called this funny behavior as the "Third joke". 

2.In this chapter Aslan calls a council to discuss the safety of Narnia, and he warns the creatures that "an evil has already entered it."

I think the question is “who is the Evil”. Aslan mentioned that the Witch is the evil.

3.What does Aslan ask Digory to do in front of the council of Beasts?

Aslan asked Digory to tell the Beasts how the evil came to Narnia.

4.From his conversation with Aslan does it seem like the enchanted writing in Charn forced Digory to ring the bell and wake up Jadis?

No, the boy admitted himself that he was only pretending to be enchanted by the writing.  He just wanted to know what would happen if he struck a bell. 

5.What does Aslan promise to do about the evil consequences which now will inevitably come upon Narnia? 

Aslan told the beasts that he would see to it that the worst falls upon himself.  I think that Aslan would try to afford the evil consequeces if happened.