§1. Witnesses must be examined at the tribunal unless the judge deems otherwise.
§2. Cardinals, patriarchs, bishops, and those who possess a similar favor by civil law are to be heard in the place they select.
§3. The judge is to decide where to hear those for whom it is impossible or difficult to come to the tribunal because of distance, sickness, or some impediment, without prejudice to the prescripts of cann. 1418 and 1469, §2.
Source: Code of Canon Law (Vatican.va)