There are two different viewport modes for a CompoComposite 2D Layer, Shape layer and 3D Layer together. [Ctrl] + [Shift] + [N] to create a new composition after opening SmodeRead More with different behaviors each: 2D and 3D.
Post-effects are not applied in the 3D mode, which can make them faster to compute.
Double click on the 3D viewport to go in four splitted views mode:
Visualizer (Green arrow)
To see only an element or a modifier of the composition you can engage the visualizer mode which is the green arrow by the side of each Layer and Modifier.
This will allow you to see only the selected element :
If you engage this tool on a modifier then you'll be able to see the layer on which it is applied in a two state mode, before and after the modifier had been applied :