In the film "The Omen", where does Damien's father discover the 'three sixes' birthmark on his son?

Damien's father (Robert) finds the 'three sixes' birthmark on Damien's scalp while he is sleeping. Robert is then attacked by Mrs. Baylock, whom he stabs to death. Armed with daggers, Robert drives Damien to a cathedral. His erratic driving draws the attention of the local police. At the church, Robert drags a screaming Damien onto the altar. He then tries to stab Damien but is shot to death by the police before he can do so.

The film "The Omen" is a 1976 supernatural horror film that was directed by Richard Donner and written by David Seltzer. It is an international co-production of the UK and the US. It stars Gregory Peck, Lee Remick, David Warner, Harvey Spencer Stephens, Billie Whitelaw, Patrick Troughton, Martin Benson, and Leo McKern.

The film's storyline follows Damien Thorn (Stephens), a young child replaced at birth by his father (Peck), unbeknownst to his wife (Remick), after their biological child dies shortly after birth. As a series of mysterious events and violent deaths occur around the family, Damien enters childhood. His parents come to learn he is in fact the prophesied Antichrist.