Listening Part A can be a conversation between any one of the healthcare professionals who can take OET and a patient or relative of the patient.
A conversation could be between a physiotherapist and a patient, an optometrist and a patient, even a vet and the owner of a pet, so before you take the test, you may need to understand words from other fields of healthcare.
It’s a good idea to learn vocabulary which is really common to the other OET professions as it is likely to come up in Part A. This vocabulary is also very often common to patients.
For example, for podiatry you could learn the names for different parts of the foot; for dentistry you could learn the different parts of the mouth and teeth etc.
If you know any colleagues or friends in these professions you could ask them for their most frequently used words, or you can do an internet search for commonly used words in another healthcare profession.
Learning around 10 words for the 12 professions is not going to be a waste of time, especially as it might help you pass the test, but you might need to use these words in your career as well.