The professional knowledge in the teacher recruitment examination refers to the professional knowledge of the subject you want to take.
For example, if you want to take an examination of primary school Chinese in a certain area, you need to take two exams. One is comprehensive education, including pedagogy, psychology, teachers' morality, current affairs and politics. The other is Chinese major, including main knowledge and teaching materials and methods.
If you don't understand anything, you can consult the online teacher of Fujian Education Network.