Albert Barnes on Titus 3:13

Bring Zenas the lawyer. This person is not elsewhere mentioned in the New Testament, and nothing more is known of him. He belonged, doubtless, to that class of persons so often mentioned in the New Testament as lawyers; that is, who were regarded as qualified to expound the Jewish laws. Mt 22:35. It does not mean that he practised law, in the modern sense of that phrase, he had doubtless been converted to the Christian faith; and it is not improbable that there were Jews at Nicopolis, and that Paul supposed he might be particularly useful among them.

And Apollos. Acts 18:24. He was also well-skilled in the laws of Moses, being "mighty in the Scriptures," (Acts 18:24,) and he and Zenas appear to have been travelling together. It would seem that they had been already on a journey, probably in preaching the gospel, and Paul supposed that they would be in Crete, and that Titus could aid them.

Diligently. 2Ti 4:9. Gr., Speedily; i.e., facilitate their journey as much as possible.

That nothing be wanting unto them. Nothing necessary for their journey. Paul desired that they might meet with hospitable treatment from Christians in Crete, and might not be embarrassed for the want of that which was needful for their journey. It would seem most probable that they had been sent by Paul on a visit to the churches.