The Catechism in Questions & Answers

521. When did the anointing of Jesus with the Holy Spirit occur?

After the baptism of Jesus, the Holy Spirit descended upon Him. John the Baptist attested the following: “I saw the Spirit descending from heaven like a dove, and He remained upon Him” (John 1: 32). This event can be described as “anointing”.

Baptism of Jesus: see Questions 129. et seq.

“Do not labour for the food which perishes, but for the food which endures to everlasting life, which the Son of Man will give you, because God the Father has set His seal on Him.”
John 6: 27