The answer to the riddle "what two keys can't open any door?" is "a donkey and a monkey."
This is because the riddle is a play on words, and the word "keys" can have multiple meanings. In addition to referring to physical objects used to unlock doors, "keys" can also refer to musical keys or types of encryption keys used in computer security.
Donkeys and monkeys, on the other hand, are animals and have no ability to open doors with physical or metaphorical keys. Therefore, they are the correct answer to the riddle.