Only PCs have courses. NPCs have a block of statistics that fully covers everything they can do. They may have functionality in common with the PC classes, but they may have additional functionality that a PC cannot replicate, or lack functionality that a similar PC has.
Referring to the basic rules for 5E (reproduced in the Monster manual), we get the following statement:
A monster's statistics, sometimes called its statistics block, provide the essential information you need to run the monster.
That's it … fun and simple. There are no extra things to look for, no progress charts to look at. Just look at their statblock, and it contains everything they are capable of.
(I understand where the confusion comes from … 3.5E had "NPC classes" like the Aristocrat, the Expert, the Warrior, etc. Nothing like this is in 5E)