I know the idea that 'on' is more accurate than 'about' but I don't know where to use them yet or if I use them interchangeably. These are examples I made up:
a film ___ the WW2.
what did you like ___ the game?
he always talk ___ money.
her lesson was ___ Spanish literature.
One of the primary definitions of "about" is "of; concerning; in regard to:" With this in mind, "about" is the main choice for all your examples.
The main definition of "on" is found in sentences like "The book is on the table." Clearly different.
When "about" is replaced by "on", it's an abbreviation of the phrase "on the topic of".
Topic: "a category or general area of interest."
This helps to explain why you can use "on" for some sentences but not others. "WW2" is a broad topic. You can have a film on the topic of WW2. However, the "game" isn't a topic, it's a specific event, and so you don't talk about "the topic of the game". No. You just talk about the game itself.
Of course, words are flexible, and by some definitions anything could be a topic. For the purposes of this question, we must consider topics to be broad, general categories.
If someone were giving an academic lecture about something, then "on" is more likely to fit, because the lecture will be "on a topic". However, if a person is talking directly to you about something specific, it's more likely to be "about", because we imagine it will be more focused on an object, and not so generalized.
"a film ___ WW2." Either "about" or "on" is possible.
"what did you like ___ the game?" Only "about", not "on".
"he always talks ___ money." Only "about", not "on".
"her lesson was ___ Spanish literature." Either is possible.
