When creating or editing an event type in your Scheduling, it's easy to add your own custom field for new bookings. This allows you to show a custom question/field for people to fill out when they are scheduling a new booking with your company.
Adding a custom question
Navigate to your advanced settings for an Event Type and click the toggle for "Additional Question". Here you can click to edit the question itself.
You can also click the gear icon to set it as a required field for your bookings as well:
How it looks
Once you've added your custom field, it will be shown right below the Name/Email fields that is part of confirming a booking.