Good question! Here's the breakdown:
What do you want to use the spoon for?
✅ Correct and natural. This is the most common and conversational way to ask the question in English.
What for do you want the spoon?
❌ Grammatically odd and unnatural. While "what for" can sometimes appear at the end of a sentence (e.g., "What is this for?"), placing it at the beginning in this way is awkward in modern English.
Alternative Phrasings:
To translate "¿Para qué quieres usar la cuchara?", you could also say:
Why do you want to use the spoon?
What purpose do you want the spoon for?
What do you need the spoon for?
Among these, the first option, "What do you want to use the spoon for?", is the most natural and widely used in casual and formal contexts.