I say, and with Allah's success: The person in i'tikaf should engage in reading the Quran, hadith, knowledge, teaching, the biography of the Prophet (peace be upon him), the stories of the prophets (peace be upon them), the tales of the righteous, and writing about religious matters. Speaking about anything other than good is disliked for someone who is not in i'tikaf, so what do you think about the one who is in i'tikaf? Refer to: Al-Tabyin 1: 351, and Allah knows best.