If the dialogue includes Socrates, it's going to involve lots of questions and answers, exploring various dimensions of the topic. You might want to pick your "person of interest" based on that person's adherence to a belief that Socrates would have found interesting, confusing, or, at any rate, worthy of exploring and understanding.
If you chose to have Socrates dialogue with Thomas Jefferson, for example, they might discuss how democractic principles can be applied to the shaping of a government; they might explore the impacts of slavery upon a society; they might consider how the differing needs of a group of people and the resulting conflicts can be most acceptably resolved.
Once you establish your belief topic and who is conversing with Socrates, your dialogue could start with your "person of interest" stating his/her opinion regarding the belief. Socrates, naturally, would respond with a question seeking to clarify or expand on some aspect of the opening statement. The conversation would continue from there.
Thank you :)