In Unhinged, Omarosa Manigault Newman -- an ordained Baptist minister -- says that Trump suggested to her that he might take the oath of office on The Art of the Deal instead of the Bible. She says that she talked him out of it, and that he made as if he had been joking. She goes on (p. 196):
...Donald Trump has no knowledge of the Bible at all. It might as well be a paper brick to him. “We love the Bible. It's the best,” he said during the campaign. “We love The Art of the Deal, but the Bible is far, far superior.” How would he know? He says he never reads the Bible. When asked, he can't recite his favorite scripture or name the books (remember when he quoted from “two Corinthians” during the campaign?). I'm not saying the president has to be a biblical scholar, but he should be biblically aware. Since the Bible has little significance to him, it might have felt disingenuous to him to take an oath on it. But The Art of the Deal meant a lot to him. Nothing has more meaning to Donald than himself.