Theophylact of Ohrid

And Jesus asks the blind man so that they would not say that He gives something other than what the blind man wanted.

Commentary on Mark ↗

Gregory the Dialogist

And it should be noted what He says to the blind man as he approaches: "What do you want Me to do for you?" Did He who was able to restore light not know what the blind man wanted? But He wishes to be asked for that which He foreknows both that we will ask and that He will grant. For He urges us persistently to prayer, and yet says: "For your heavenly Father knows what you need before you ask Him." Therefore He requires to be asked for this reason: He requires it in order to arouse the heart to prayer. …

Forty Gospel Homilies, Homily 2 ↗

Bede

And Jesus, responding, said to him: What do you want me to do for you? The blind man said to him: Rabboni, that I may see. Did the one who could restore light not know what the blind man wanted? But he wants this to be requested, which he foresees that we should ask and that he should grant. For he persistently urges us to prayer and says: For your Father knows what you need before you ask him (Matthew 6:8). Therefore, for this reason, he requires that it be asked; for this, he requires that the heart be stirred to prayer. …

On the Gospel of Mark ↗