These final words from the bible would be the point I would suggest Catholics begin their study of the book.
Revelation 22:18
I warn everyone who hears the words of the prophecy of this scroll: If anyone adds anything to them, God will add to that person the plagues described in this scroll. 19 And if anyone takes words away from this scroll of prophecy, God will take away from that person any share in the tree of life and in the Holy City, which are described in this scroll.
20 He who testifies to these things says, “Yes, I am coming soon.”
Amen. Come, Lord Jesus.
21 The grace of the Lord Jesus be with God’s people. Amen.
When the Apostle John says “this scroll” what do you imagine he is referring to?