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

The Uncle Andrew was all in black except for his white waistcoat and the great grey mop of his hair didn’t look to them like anything they had seen in the three other humans.

Then Uncle Andrew dropped down in a dead faint,Jackdaw thought it was very funny so he call 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."

An evil witch

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

He ask Digory to tell all of the council od Beasts how the evil witch came here and for what purpose that he did it.

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, he said he was only pretending.

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

He said he will prmise the worst falls upon himself.