I've read 9 of his books - he's mentioned in many of them that he only sleep around 4 or so hours/night then he gets up and reads a lot of newspapers plus a variety of magazines to keep on top of economic, political and cultural events around the world. He would share anything relevant or interesting with his staff when he got to the office. He's totally amazing!
Out of the 9 books that I've read by POTUS, I'd recommend the following for anyone who'd like more insight into his life, how he thinks etc (the first 2 are obvious):
The Art of the Deal 1987
Great Again 2015
Time to Get Tough 2011
Trump: How to Be Rich 2004 - which is a great look into the different aspects of his life
I'd also highly recommend Don Jr's book "Triggered" - a fascinating read….I couldn't put it down!