It depends. If you do not know what word to use then it is "Как сказать?". If you know a word but are unsure about its correct pronunciation then it is "Как произнести правильно?"

Как сказать "a dog" по-русски? (What is is the Russian word for "a dog"?)(I do not know this animal's Russian name.)
Как правильно произносится "выкарабкивающихся" ? (I know the meaning, I can recognize this word on a page, but I am unsure how to say the word correctly.)