Jesus told Nathanael he would see the angels of God doing what on the Son of Man?

Answer: Ascending and descending

Jesus promised Nathanael greater things: heaven open and the angels of God ascending and descending on the Son of Man.

“Jesus said to him, “Do you believe just because I told you I saw you under the fig tree? You will see greater things than these.” Then He declared, “Truly, truly, I tell you, you will all see heaven open and the angels of God ascending and descending on the Son of Man.””— John 1:50-51 (BSB)