I don't know a way to manually edit the autotype dictionary, but my iPhone has definitely learned new words from me. For example, it knows that I like to type the word "redscull" and will autocorrect my typing to spell it for me when I make a typo. And obviously that's not a real word.
I'd be more interested to know how to unteach the dictionary. I've accidentily taught it some mispelled words that I'd rather it quit autocorrecting my typing to.