3 witnesses of Christ here, and 2 further echoes from the reading.
Christ — the Anointed One
And it came to pass that Alma said unto him, taking him by the hand: Believest thou in the power of Christ unto salvation? Alma 15:6
Before healing him, Alma asks Zeezrom whether he believes Christ has power to save. Healing starts with faith in Jesus Christ.
How we know: the verse itself names Him
Christ — the Anointed One
And Alma said: If thou believest in the redemption of Christ thou canst be healed. Alma 15:8
Alma ties Zeezrom's healing to belief in Christ's redemption, His Atonement. The fever was caused by guilt, so the cure is the Redeemer who takes away sin.
How we know: the verse itself names Him
Christ — the Anointed One
And then Alma cried unto the Lord, saying: O Lord our God, have mercy on this man, and heal him according to his faith which is in Christ. Alma 15:10
Alma asks the Lord to heal Zeezrom because of Zeezrom's faith in Christ. Mercy comes to him through Jesus Christ.
How we know: the verse itself names Him
And when Alma had said these words, Zeezrom leaped upon his feet, and began to walk; and this was done to the great astonishment of all the people; and the knowledge of this went forth throughout all the land of Sidom. Alma 15:11
The healed man leaping to his feet and walking matches the lame man Peter healed in the name of Jesus Christ. Healing through faith in Christ works the same way in both hemispheres.
And Alma baptized Zeezrom unto the Lord; and he began from that time forth to preach unto the people. Alma 15:12–13
Zeezrom and many others are baptized 'unto the Lord,' making covenants with Christ. Baptism symbolizes being buried and raised with Christ, so it points to His death and Resurrection.