Learn French: Tu prends un bon sandwich pour le déjeuner ? - Are you having a good sandwich for lunch?

When talking about food and drinks, French uses the verb prendre (to take) instead of "to have" or "to eat". So Tu prends un sandwich literally means "You take a sandwich", but we naturally translate it as "You are having a sandwich."

Do you pronounce the "d" or "s" at the end of prends?

No, the -ds at the end of prends is totally silent. It sounds exactly the same as the "I" form, je prends. You just pronounce the nasal vowel sound, similar to "prahn".

I thought French adjectives went after the noun. Why is it un bon sandwich and not un sandwich bon?

While most French adjectives do go after the noun, a small group of short, common adjectives go before it. These are usually adjectives that describe Beauty, Age, Goodness, and Size (often remembered as BAGS). Since bon (good) describes goodness, it goes before the noun.

How is this a question if there is no question word like est-ce que?

In casual, spoken French, it is very common to ask a yes or no question by just using normal statement word order (Tu prends...) and making your voice go up at the end. You could also say Est-ce que tu prends..., but this shorter way is perfectly natural for everyday speech.