I imagine you would talk about anything you would talk about on any other first date. No one is sitting with you, you are basically on your own. So think about what you really want to know about the other person and what is important for you to hear for yourself.
Do you want to know what hobbies they have? What they like to do when they have a few minutes off from their normal routine? Do you want to know what their normal routine or seder hayom is like? Do you want to see if the two of you are alike in any way? Maybe you would want to know what their favorite color is, or if they like flowers, or if they like kids? Ask what age kid they think is most fun. Ask about their siblings, ask about their grandparents. Watch their responses. Are they happy and excited when they speak about their siblings and grandparents? Do they show respect and ahava for their family? These are important signs to watch for.
These are pretty much “warm” and safe things to talk about, but they are questions that should bring about good discussion and allow you to have a peek into the other’s personality. If they tell you a story about a member of their family it might give you a hint of their sense of humor.
You can ask questions like what values do you look for in your best friend. This will give you a peek into the other’s value system. Ask open ended questions to give the other person a chance to talk and not just say yes or no. So stay away from “do you like chocolate? Yes? Me too!