Peter was told by the servants of Cornelius why he had sent for him (see Acts 10:22). He knows that he must come to tell him about Jesus Christ. By asking Cornelius this question, he gives him a chance to recount his visit with the angel so that everyone present is on the same page and ready to hear Peter’s message.1
29 C'est pourquoi je n'ai pas eu d'objection à venir, puisque vous m'avez appelé; je vous demande donc pour quel motif vous m'avez envoyé chercher.