Bobk has explained to me the difference between 'knowledge of' and 'a knowledge of', but I still feel confused. I've added three sentences and phrases to my original post and was hoping native English teachers could kindly further help me to solve this problem of mine. Thank you very much in advance.
1. He has a wide knowledge of painting and music. (OALD, 6 edition, knowledge)
2. Knowledge of French is a plus in her work. (OALD, 6th edition, plus)
3. Solicitors should possess detailed knowledge of certain aspects of the law. (Macmillan, knowledge)
4. They seemed to have inside knowledge of MI5 operations. (Macmillan, inside)
5. They are salesmen with good technical knowledge of what they're selling. (LONGMAN 4 edtion, knowledge)
6. An in-depth knowledge of accounting is not necessary as training will be given. (LONGMAN, 4 edition, knowledge)
7. The year studying in the US gives students personal knowledge of American culture. (LONGMAN, 4 edition, knowledge)
8. Candidates must have a good knowledge of chemitry. (LONGMAN 4 edition, a)
9. She has theoretcal knowledge of teaching, but no practical experience. (LONGMAN 4 edition, theoretcal)
10. someone with a background knowledge of engineering (LONGMAN, 4 edition, knowledge)
From these sentences I guessed that 'knowledge of...' equals 'a knowledge of'. But I'm not sure.
Could I ask native English teachers to help me with this question?
Thank you very much again.
Either is correct grammatically.