When answering “Qui décide ce qui est beau?”, do you use “I do” as in “je fais” or “oui” as in “yes”? Can you also answer with “je décide”?
There are a few options. Usually you will use the emphatic pronoun moi (also called the disjonctif).
For example, you could say any of these depending on how verbose you want to be:
C'est moi qui décide.
The emphatic pronouns are je / moi, tu / toi, il / lui, ils / eux (elle, nous, vous, elles don't change).
You could also just use je but it would be less likely to appear without the emphatic moi :
Moi, je décide.
If you want to say something like "I do", you have to use le (literally "I do it"). This is true every time you want to replace a verb with "do". The same thing about moi applies here too.
(Moi) je le fais.
You can't reply with just oui because this is an open-ended question, not a yes/no question. The following exchange makes no sense in either English or French.
Qui décide ce qui est beau ? Who decides what is beautiful?