The seeing points specifically to the visions that Amos saw though it also refers to the book as a whole. These visions are recorded in Amos 7:1 – 9:15. As with other old covenant prophets, Amos was given insights and revelation from the divine council (Jeremiah 23:18–22).1
1 The words of Amos, who was among the shepherds of Tekoa, which he saw concerning Israel in the days of Uzziah king of Judah and in the days of Jeroboam the son of Joash, king of Israel, two years before the earthquake.