Learn Spanish (Latin America): ¿No comes carne? Entonces comemos pescado.

Spanish doesn't use helper words like "do" or "does" to make questions. To turn the statement No comes carne (You don't eat meat) into a question, you simply add question marks and raise your voice at the end: ¿No comes carne?

I don't see the words for "you" or "we" here. How do we know who is eating?

In Spanish, the ending of the verb tells you who is doing the action. Comes ends in -es, which tells us the subject is tú (you). Comemos ends in -emos, which tells us the subject is nosotros (we). Because the verbs make it clear, the pronouns are safely dropped.

Could I use pero (but) here instead of entonces (then/so)?

You could, but it completely changes the meaning! Entonces shows a result or a solution: "You don't eat meat? So (as a result) we eat fish." If you used pero, it would sound like a contrast: "You don't eat meat, but we eat fish."

Why is it just carne and pescado instead of la carne and el pescado?