My personal list:

• What exactly do the functions do?
• Example usage of every function with use case.
• What format/type are the input parameters?
• Is it cached by jussi?
• Rough time complexity for the rpc node to process it?
• What do we get back?
• What errors to expect and how to handle them?
• When to retry and when to fail?
• How do prices works? STEEM ⇔ SBD ⇔ USD what is what in the market objects?
• How to get accurate voting power?
• How to calculate how much an upvote is worth?
• What are transactions, what are blocks, what are operations, what are virtual ops?
• What extra data is in every block and how to use it?
• How to ensure you do not double send a transaction?
• How to ensure you really send a transaction?
• Probably a lot more, but these are a good start in my opinion.