Can the words”ce que/ce qui/ça” be used to refer to something previously mentioned?

Yes, but not as illustrated in your examples. Let’s fix them.

Nous allons parler de ce que.

que here is referring to something coming after, so the sentence feels like it has been truncated. A correct one would be:

Nous allons parler de ce qu’il s’est passé. (Let’s talk about what happened.)

A similar example would be the colloquial:

Pour faire valoir ce que de droit. (For all due intents and purposes.)

You probably intended to say something like:

Nous allons en parler. (We will talk about it.)
Nous allons parler de ça. (We will talk about that.)

En ce qu’un seconde “In that one second”

Again, the example feels truncated or a part is missing. I interpret the meaning more like “In what would have taken one second.”

You can say instead:

En cette seconde. (During that second, or From this instant, depending on context.)

Je suis désole si c’était stupide.

Ironically, this one is correct, except for the missing accent at désolé.