Discovered that I need to add a line of code to the Content-Page.cshtml (same one that sets the page Title) and set the dynamic variable "Layout" to support ContentItem.
(e.g. Layout.ContentItem = Model.ContentItem)
Now I have access to ContentItem from within the Layout.cshtml.
When not using the Content-Page.cshtml alternate; the ContentItem is still null; so I'm not sure how everyone else's is not null unless they are setting it elsewhere.
Hope this helps someone.