Can't figure out how to get Onion Skin to work

Hey, just trying to figure out why my onion skin setting isn't working. Basically, I had an object on one layer, in the timeline:

-and I planned to use onion skinning to animate on another. However, last time I did this, (different computer, probably different version) onion skin worked fine, but I couldn't see why it wasn't working this time.

I did check onion skin settings in case something was awry, but I didn't see anything I thought would be causing this.

Not sure what to do, or if I'm missing something here? Thanks.