I'd like to ask George if he ever really believed in the dream he shared with Lenny for so long.
Another two questions for George:
How do you feel about Lenny, deep down? Is he a friend you are glad to have or a burden?
What will you do now, with Lenny dead?
I would want to ask Curley's wife a series of questions as she is unable to have a conversation with anyone in the novel - she recoils into crude threat when realising she is left behind with the rejects when the others go to town, and her brief and tragic interaction with Lennie proves fatal.
What had she hoped life would be like on the ranch?
How did she cope with the rejection of everyone around her?
Did she choose Curley out of love or desparation?
I would ask George why he feels responsible for Lennie. The two men are friends and are not related, but George sticks by Lennie and protects them. Living with Lennie is difficult, and Lennie holds him back, but he does it anyway. He would do anything for Lennie. Why?
Slim, who has "God-like eyes" and "hears what is not said," is probably the character who is most aware of the dynamics of the men in the bunchhouse and cognizant of the problems that the itinerant workers incur psychologically. So, after concluding questions to the other characters, you may wish to interview or re-interview Slim, asking him (1) to explain what he feels is greatest problem among the ranch workers, and how this problem can be solved. (2) Also, you could ask him his position of the shooting of Lennie and why he told George, "You hadda, George, you hadda."
I'm not sure which characters you'll be playing in class, so I've suggested a few questions for all of the characters, based on what I'm teaching to my students at the moment. I also put in brackets the subjects you could try to develop through further questioning:
1. Why did you allow your dog to be shot? Do you regret it? Why do you think you should have shot him yourself? (remembering that the shooting of Candy's dog foreshadows Lennie's death, and raises ethical questions on the treatment of both the dog, and, more importantly, Lennie).
2. Why would you share all of your money with Lenny and George in order to buy the farm, when they have less money than you? (thinking about Candy and how he represents less fortunate migrant workers)
1. What would a life on George and Lennie's farm offer you?
2. If you could, would you live in the bunkhouse with everyone else? (think about Crooks' love of books and comfortable life in the stable, versus his human need for companionship)
1. Why do you like to fight other men? (thinking about his need for security, both as a person, and in his marriage)
2. Do you think you would have had a happy marriage if your wife was still alive? (thinking about Curley and his wife's temperaments)
For Curley's wife:
1. What is your greatest dream in life? (Steinbeck develops her character by telling us she wants to be a movie-star)
2. Why did you decide to marry Curley? Do you think you will have a happy marriage together? (Does Curley's wife seem like the domestic type? Would she enjoy having a family?)
1. Why did you decide to look after Lennie, when you used to treat him badly? (George feels guilty about his past treatment of Lennie, and wants to change and be a better man - a character who evolves through the book, echoing Steinbeck's beliefs that mankind can be perfected)
2. Did you really believe in the dream of the farm? (Aiming to discuss whether Lennie help George to believe in a better world, and whether George secretly knows this is unrealistic.)
3. Will you stay at the ranch, now that you don't have to move around with Lennie? (Explore the friendship with Slim, and feelings of relief and/or regret).
1. Do you think you will ever change? (thinking about Lennie's character in the book - is he a flat or a very detailed character?)
2. Why would you like living on the farm, apart from the rabbits? (development of character, social issues such as discrimination, and topics of friendship and responsibility, concerning George)
2. Why do you think George tells you what to do if you get into trouble again? (discussion could lead to more discussion on foreshadowing, and George's attempts to protect Lennie)
1. Do you enjoy working on the ranch? (chance to talk about social conditions and other characters)
2. Do you think George was right to shoot Lennie? (ethical issues)
I hope some of those ideas interest you for your class discussion!