So, I actually tried it out today and here are two things to do to make sure everyone understands:
After they have found most of the punchlines, (A has the hardest time of this, C seems easiest), get them to sit down in groups (A, B and C). Start with A - they probably won't have all the answers, so go over the questions with them to be sure they understand and see if they have the right punchline. You may need to explain the jokes a bit too, then laugh as if it's the funniest thing you ever heard. Note - when you are going over the answers with one group, the other two groups are alone... maybe ask the co-teacher to watch them so they don't burn down the classroom or something.
Sometimes the kids (especially the ones with A page) will need to go back for a second try (while you go talk to B and C).
Then, get them into pairs to exchange jokes (only about 2 or 3 minutes on this). If they need a roleplay, try:
1-Let me tell you a joke.
2-Go ahead, I'm all ears!
1- JOKE (Student picks a joke to tell from their page)
2- LAUGH
...then change roles.
The whole activity, including instructions etc, lasts about 25-30 minutes.