It is permissible to supplicate in the last rak’ah of Salatul Witr before [ Source: Abu Dawud.] or after rising from bowing [ Source: Al-Bukhari.].
The hands are raised and supplications (reported from the Prophet) are said. For example: “Allahummahdini fiman hadayta, wa ‘aafini fiman ‘aafaita, wa tawal-lani fiman tawallaita, wa baarik li fima a’ataita, wa qini sharra ma qadaita, fa innaka taqdhi wa la yuqdha ‘alaika, innahu la yadhillu man walaita wala ya ‘izzu man ‘aadaita tabaarakta Rabbana wata ‘alaita.”Meaning: “Oh Allah, guide me along with those whom You have guided, pardon me along with those whom You have pardoned, be an ally to me along with those whom You are an ally to and bless for me that which You have bestowed on me and protect me against the evil of what you have decreed. For verily, You order and none can order You. For surely, he whom You show allegiance to is never abashed and he whom You take as an enemy is never honored. O’ our Lord, Blessed and exalted are You.” [ Source: At-Tirmidhi.]