Is onion skin the part where you see the frames that you have already drawn? if so, How do you make it so that you only see 2 frames at a time? The previous frame and the frame you are on.
The previous/next onion skin can be turned on/off separately in Display window (Ctrl+5 to bring it up).
And you can change the number of onion skins in Preference. Set the number to 1 if you only want to see one previous frame.