Some narrations mention that Allaah The Almighty sends an angel to a place while mentioning the phrase "Allaah knows best" which means that Allaah The Almighty knows the news that the angel will bring. What is the wisdom for sending an angel while we all believe that Allaah The Almighty knows everything and the angel will come with something that Allaah The Almighty already knows?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

Perhaps you mean what is mentioned in the Hadeeth (narration) that was narrated on the authority of Abu Hurayrah that the Prophet, sallallaahu ‘alayhi wa sallam, said: "There are angels who take turns in visiting you by night and by day, and they all assemble at Fajr and ‘Asr Prayers. Those who have spent the night with you ascend to the heavens, and their Lord, who knows better about them, asks: 'In what condition did you leave My slaves?' They reply: 'We left them while they were performing prayer and we went to them while they were performing prayer.'" [Al-Bukhari and Muslim]

Also, it was narrated on the authority of Abu Hurayrah that the Prophet, sallallaahu ‘alayhi wa sallam, said: "Allaah has angels who look for those who celebrate the praises of Allaah on the roads and paths. When they find some people celebrating the praises of Allaah, they call each other, saying, 'Come to the object of your pursuit.' Then the angels encircle them with their wings up to the sky of the world, and their Lord will ask them - although He knows better than them - 'What are My Slaves saying?' The angels will reply, 'They say: Subhaana Allaah, Allaahu Akbar, and Alhamdu-lillaah.'" [Al-Bukhari and Muslim]

Al-Haafith ibn Hajar commented on the first Hadeeth, saying, ‘By "He Asks them", it is said that the wisdom behind this question is to call their witness to the children of Aadam (Adam ) and to incite them to utter words that causes them to be shown mercy. Also, the question is made to manifest the unique wisdom of Allaah behind creating mankind regarding whom some of the angels said to Allaah The Almighty: {Will You place upon it one who causes corruption therein and sheds blood, while we declare Your praise and sanctify You?" Allaah said: "Indeed, I know that which you do not know.}  [Quran: 30]

It means that there are some people who glorify and sanctify like you according to your testimony. ‘Iyaadh said, "Such a question was addressed as an act of worship to be carried out by the angels, exactly as they are commanded to record the deeds of the children of Aadam, although Allaah The Almighty is the most Aware of all."

You bear no sin by asking this question, for this pertains to seeking understanding of the religion. Islamic texts actually praised seekers of knowledge. We ask Allaah The Almighty to increase your knowledge and grant you success.

Allaah Knows best.