Please could you indicate where it is located this Developer Documentation about Workspaces?

If you login to workspaces as administrator can you download the documentation and sample widget library by clicking on the URL links in the Overview section of the Workspaces Administrator widget?

...and where is this documentation if you dont have workspaces installed yet or access to administrator level on a deployment?

I am struggling to find a point of reference on Avaya site for the whole Workspaces development environment and process or technical detail to allow me to design a solution for a customer where widgets require developing to provide event handling and back end integration.

I think that's correct, you can only access it if you have the product and appropriate support from people with administrator access. You may also be able to get it through sales and consultancy channels (I don't know, TBH) but they have chosen not to publish on DevConnect at this time.