Have a look at my screen shots please:

http://pasteall.org/pic/33a3b4a05c6db62 ... e9de24a3c8

http://pasteall.org/pic/7d6d023059fd9cc ... a0f84ead73

Thanks

To have onion skins, the layer must have been made into an animated layer, with frames on the timeline docker. When you select a layer, it appears on the Timeline docker but it's not animated until you create the initial frame (frame-0) with Create Blank Frame or Create Duplicate Frame.

Then, the onion skin 'lightbulb' icon will appear on the layer entry on the Timeline and in the Layers docker. Clicking this icon, in the Layers docker or the Timeline docker will turn on the onion skins display for that layer.

The onion skin checkbox also appears on the Properties view of the layer and can also be used to turn the onion skin display on and off for that layer.

Excellent!
Thank you ahabgreybeard