What am I doing wrong? Using 2.81 Windows 10. Onion skins do not appear in draw mode, but they do appear in edit and sculpt. When I load the same file into 2.80 the onion skins appear in draw mode.
As you can see (top image) Onion Skins are checked in Viewport Overlay, and the layer (Mr C) also has onion skins checked, so too are they checked in the materials tab.
And in Blender 2.80 opening the same file (bottom image) the onion skins show.
When I open up a new blank file in 2.81 and draw with grease pencil the onion skin works fine in draw mode.