I'm not clear what you are asking. The plug-in is a commercial third-party tool totally outside of Adobe. You have to buy it.
You can set up your own onion skin with a duplicate of your layer using a script or expression: AE ENHANCERS • View topic - Onion skin
Maybe a better way to to it is explained in this series from Lynda.com: Onion skinning. It uses Photoshop for video.
If you are hand drawing animation AE can be a great tool for some styles but there are other apps much better suited to others. It all depends on your style and your goals.
I'm in the same boat as the first poster and running into headaches.
Not sure if the problem lies with my slow machine or the process I'm using but I'll try to explain.
I shot some video and I'm trying to make little animations over it. Like this: ScHoolboy Q - THere He Go (Official Video) - YouTube
The tutorials I've seen tell me to build my video in Premiere and export the clips I want to draw over into After Effects. But, when I get to After Effects with my clip, and i start to draw on one frame, when I go to the next I have no reference of what I drew before except memory. Its hard to make things line up and it looks crappy, and jumpy.
In photoshop there is an Onion Skin feature. I looked on the Lynda tutorial and found out about it and started exporting the clip from After Effects to Photoshop as a PNG, and then drawing on each PNG in photoshop using onionskin when needed and then importing the .PNG files back into Premiere. Is there a better way to do this????