How do you say What is for dinner in sign language?

You can't directly translate "What is for dinner?" into a single sign in American Sign Language (ASL). It's more natural to express it using several signs. Here's one way to do it:

1. "What" (sign for "what")

2. "Eat" (sign for "eat")

3. "Tonight" (sign for "tonight" or "this evening")

You can also use the sign for "food" instead of "eat".

You would then use the appropriate facial expressions and body language to convey the question and make it clear you are asking about the meal.