"Say it clearly!"
So "it" is usually translated to "o" only if it is a subject? Through the whole course "o" = "it/he/she," and in a combination with a noun "that," therefore it was also my first guess to use "onu" in this sentence.
I don't see an answer to Simon62188's question, so: Why is "Açıkça de" wrong?
I am learning too, so I am not really sure. I think that it is a set phrase. You are saying here that somebody should say open, frankly his opinion and not that he may pronounce a word better, clearer. I think therefore is used söylemek here. Demek would be used if you refer to a clearer pronounciation. May anybody correct me if I am wrong