The important thing for US president to know is the roughly 30 pages of Constitution and its amendments, also key Supreme Court interpretations of Constitution by justices who respected state sovereignty. Likewise for constitutional lawmakers who respected 10th Amendment-protected state powers. Also include key excerpts from writings of founders like Madison and Jefferson who respected state sovereignty.
As a side note concerning the need for a president who knows how to run a thriving business, historical profiles indicate that self-made millionaires like Cornelius Vanderbilt and John D. Rockerfeller never had a formal college education, Vanderbilt quitting school and age 11 and Rockerfeller spending several months in a formal bookkeeping course after high school.
But also note that the states have never delegated to the feds, expressly via the Constitution, the specific power to regulate intrastate commerce. So maybe all that a president needs to lead Congress with respect to treaties and trade negotiations is uncommon common sense.
Otherwise, military issues aside, basicall the only domestic issue that a president is constitutionally authorised to sign bills for is US Mail Service policy (1.8.7). And that arguably doesn’t require a college degree.
IIRC, George Stephenson (the guy who invented the railroad) never went to school at all. He started working when he was five years old and had to hire a tutor to learn to read when he was about 20.