You could try checking if there is any literature related to the field, which may give you some ideas for topics to ask about. Without knowing anything about the field, I would ask:
- Can you explain what is involved with pregnancy massage (PM)?
- What are the benefits and risks involved with PM?
- Are there any special safety considerations involved with PM?
- What training and experience is required to offer the service?
- What is the best thing about providing this type of service?
Hope that gets you started.