It would be more natural to say: I don't want to express my opinion without knowing more about it first or I don't want to say anything until I learn more about it Your sentences would be better and more natural if you used 'knowing more' instead of 'knowledge'

I would say, "I don't want to express an opinion on something I know nothing about. But that doesn't seem to stop any politicians." 8-D

of, on or about the subject. I do not want to give my opinion without further research on the subject. express is fine - knowledge is fine, yet the sentence above is more likely used. By saying research, you avoid admitting you do not have the knowledge, and let the listener not know what questions you need answered.

I don't want to express my opinion if I don't have all the facts. I don't want to express an opinion without full knowledge about the subject. I don't want to express an opinion without knowing all the circumstances about the incident. I don't want to give my opinion without knowing more about the topic.

Only the first requires "about the subject" at its end to keep the same meaning of the other ones.