A main feature of the current CityEngine 2016 Basic is the get map data. This seems to be tied to a subscription.
The wizard for this has a link to trial of ArcGis Pro online but this seems excessively expensive to enable a single albeit important feature. An ArcGIS Online Subscription Level 2 is for 5 users with 2500 credits not at all appropriate for a single user of the software.
Thank you for this question about Get map data from ArcGIS Online / Portal .
A free Arc GIS Online subscription is sufficient to download Basemap and Open Street Map data.
The paid subscription is only needed for the Esri World Elevation service.
For many workflows in CityEngine this is sufficient.
For instance: KML Models are usually clamped to the ground and therefore need no exact height reference.