I haven’t looked at the curriculum but basics of Python and JS are important. Esp. Data structures like dictionaries, lists etc. in Python are important.
Even more important is to read the code already written in the Frappe/ERPNext apps. Use the doctype or report, and try to understand why the feature works like that. Reading queries from the forum and trying to help out other users will also help you learn better.
Also, since you will be interacting with the Database a lot, so learn MySQL queries (ERPNext also is probably coming up with Postgresql support)
You can buy it, use it and write more code and understand how code works - use it as a means to become better. There will always be more to learn. Best of luck !