The function table is filled in a what I call "bind function" pointed by the structure at the fskGrammar symbol. In case of ebook.so, fskGrammar -> ebookGrammar -> "bind function". That function fills the "@" array with wrapped functions, constructors and destructors, usually taken from a table with the entries of the following format:
uint16_t type; // 0: function, 1: constructor, 2: host object destructor
uint16_t nargs; // number of arguments for function or constructor
For example, in 600's ebook.so function @ is eBook_checkScreenLock, function @ is eBook_debugProcess and so on.
The actual functions all call into the Fsk bytecode machine and can be pretty hard to follow.