Sources of information worth checking out
The Speaking test is profession specific but your profession is broad. There is a good chance that the topic you role-play will not be one you would talk about everyday in your work. Although your medical knowledge is not being assessed, you will feel more confident about what you are saying if you feel you know something about the topic.
It’s a good idea to look through the notes and textbooks you will have used when you were first training for your profession. This training will likely have covered a lot of general topics before it became more specialist towards the end.
Another source of information are health websites. The World Health Organisation has a lot of useful factsheets about many health topics. You can also refer to sites aimed at the general public which will explain topics in clear English.