4 witnesses of Christ here, and 1 further echo from the reading.
Christ — the Anointed One (Greek for Messiah)
And when Silas and Timotheus were come from Macedonia, Paul was pressed in the spirit, and testified to the Jews that Jesus was Christ. Acts 18:5
Pressed by the Spirit, Paul bears plain testimony in Corinth that Jesus is the promised Messiah.
How we know: the verse itself names Him · a footnote points to Him · a Church study aid lists it
And Crispus, the chief ruler of the synagogue, believed on the Lord with all his house; and many of the Corinthians hearing believed, and were baptized. Acts 18:8
Even the leader of the synagogue puts his faith in the Lord Jesus, along with his whole family. In the context of Paul's testimony (v. 5), 'the Lord' is Jesus the Christ.
How we know: a Church study aid lists it
Then spake the Lord to Paul in the night by a vision, Be not afraid, but speak, and hold not thy peace: Acts 18:9–10
The risen Lord personally speaks to Paul in a vision, calming his fear and promising protection. He already knows the many people in Corinth who will become His.
How we know: the verse itself names Him · a footnote points to Him · a Church study aid lists it
This man was instructed in the way of the Lord; and being fervent in the spirit, he spake and taught diligently the things of the Lord, knowing only the baptism of John. Acts 18:25
Apollos knew and taught the things of the Lord Jesus, though only up to John's baptism. 'The way of the Lord' echoes the way John the Baptist was sent to prepare for Christ.
Christ — the Anointed One (Greek for Messiah)
For he mightily convinced the Jews, and that publickly, shewing by the scriptures that Jesus was Christ. Acts 18:28
Apollos uses the Old Testament to prove publicly that Jesus is the Messiah. The scriptures are a witness of Christ.
How we know: the verse itself names Him