When creating the registration page, you can define which questions are shown to each participant type. This is done by ticking and unticking the boxes on the right hand side of each question:
This can also be done in the editing window when editing an individual question. You can choose which participant types can see this question in Settings > Who can see this question? > By participant type.
The same boxes show on the right in the editing window that pops up when you click the pencil icon on a question.