Answer:
Juan quiere comerla OR Juan la quiere comer.
Explanation:
The direct object is the equivalent of saying "it" in English. Instead of saying "Juan wants to eat an apple," you must change the sentence to "Juan wants to eat it." Since una manzana is a feminine noun, you must use the feminine direct object "la." This can go in two places (both are grammatically correct): before the conjugated verb (quiere) or attached to the end of the unconjugated verb (comer).
Hope this helps!!
