I imported a tree shapefile and assigned rule to it, but when I selected the layer, I couldn't see any attribute or rule in the inspector window, (see the picture) so that I can't match the attribute table to the corresponding attributes in the rule file (height, diameter, etc.). Did I miss something?
Check the grammar and annotations for your attributes. CityEngine 2016 is a little more strict. So although the editor may not show there is an error, you'll see this behavior when you generate.
It looks like you have the layer selected, but I'm guessing you want to see the attributes from the rule file applied to the shapes in the layer. If this is the case, select a shape (click on shape in Viewport) instead. Or, you can select all the shapes in the layer (right click on layer in Scene Editor -> Select Objects). In this case, the values of the attributes will be marked with ? if they have different values for each of the shapes in the selection.