Toggling the ON eye button activates the skins, it can be a rig or object.

 

The frame range can be manipulated to show up to 200 frames backwards and forwards if needed.

 

Toggling the keyframes Only button is great at many stages

 

Not only meshes but bones can be onion skinned too, here you can alter the line thickness for clarity –

 

The visibility toggles can show only the past skins, or vice versa… use a progressive fade and other options