8. Who was the second disciple of Jesus on the way to Emmaus?

According to the most ancient Christian tradition, the companion of Cleophas on the way to Emmaus was his son Simon (Simeon), the future second bishop of Jerusalem:

Origen, Against Celsus, Book II, 62 (written in 248 AD):

And in the Gospel of Luke also, while Simon and Cleopas were conversing with each other respecting all that had happened to them, Jesus drew near, and went with them. And their eyes were holden, that they should not know Him. And He said to them, What manner of communications are these that you have one to another, as you walk? And when their eyes were opened, and they knew Him, then the Scripture says, in express words, And He vanished out of their sight .

(Ante-Nicene Fathers, Vol. 23, Edinburgh, 1875, p. 65, translated by Frederick Crombie)

St. Simeon, engraving by Diodore Rahoult

Apparition of Jesus to the disciples on the way to Emmaus (Notre-Dame de Paris)

Eusebius of Caesarea, Church history, Book III, ch. 11 (written ca. 324 AD):

"After the martyrdom of James and the capture of Jerusalem, which immediately followed, the report is, that those of the apostles and the disciples of our Lord that were yet surviving, came together from all parts with those that were related to our Lord according to the flesh. […] These consulted together, to determine whom it was proper to pronounce worthy of being the successor of James. They all unanimously declared Simon the son of Cleophas, of whom mention is made in the sacred volume, as worthy of the episcopal seat there. They say, he was the cousin german of our Saviour, for Hegesippus asserts that Cleophas was the brother of Joseph ."

(The Ecclesiastical History of Eusebius Pamphilus, translated by Isaac Boyle, Michigan, 1955, p.99 )

St. Cyril of Alexandria, Commentary on Luke, ch. 24 (written in the first half of the 5th c.):

"You must know that these two disciples belonged to the number of the seventy, and that Cleophas’ companion was Simon - not Peter or the one of Cana - but another Simon, of the seventy ."

(A Commentary upon the Gospel according to S. Luke by S. Cyril, Patriarch of Alexandria, translated by R. Payne Smith, Part II, Oxford, 1859, p. 726)

Another tradition considers St. Luke to be Cleophas' companion:

St. Gregory the Great, Moralia in Job, Preface, 3 (late 6th c.)

"…It is the manner of Holy Scripture for the persons who are writing so to speak of themselves in it, as though they were speaking of others. […] Hence Luke says, that two of them were walking by the way, Cleophas and another; which other indeed, while he was so carefully silent about him, he showed to have been no other than himself, as some assert ."

(Morals on the Book of Job by S. Gregory the Great, John Henry Parger, transl., Oxford, 1844, vol. 1, p. 15 )

Orthodox prayer for travellers

"O Lord Jesus Christ our God, the true and living Way, Who didst will to journey with Thy guardian Joseph, and Thy most pure Virgin Mother into Egypt, and didst accompany Luke and Cleopas on their way to Emmaus: we now humbly entreat Thee, O most holy Master: do Thou accompany now this Thy servant ..."

(source: https://www.oca.org/orthodoxy/prayers/prayer-for-travel )