Bitcoin Standard by Saifdean Amous if they are academic. Mastering Bitcoin by Andreas Antinopolus if they are technically proficient in computer programming, Or Programming Bitcoin by Jimmy Song if they are new to coding. 

Honestly these are advanced bitcoin books I think every bitcoiner should read, But if that is too much for you maybe go buy some gold. 

The little hodlr cartoons by Line Seiche would be good for people who are just learning to think in bitcoin instead of FIAT.