Learn Dutch: Vandaag haal ik de speciale chocolade voor hem. - Today I am getting the special chocolate for him.

Yes, you can! But if you drop the preposition, strict Dutch word order kicks in. The indirect object (hem) must come right before the definite direct object (de speciale chocolade). So the sentence would become: Vandaag haal ik hem de speciale chocolade.

Why do we use voor here instead of aan?

You use voor (for) when you are doing a favor or getting something on behalf of someone, which fits perfectly with the verb halen (to get/fetch). You use aan (to) when you are physically giving, handing, or communicating something directly to a recipient.

Why is the verb before the subject (haal ik instead of ik haal)?

Because the sentence starts with the time word Vandaag. Dutch uses the V2 rule, meaning the working verb must always be in the second position of a main clause. To keep haal in the second spot, the subject ik has to swap places with it.

Why is the adjective spelled speciale instead of speciaal?