In Zoom 5.1 and greater, Zoom can read all of the layers inside a Photoshop document automatically. This allows you to view the Layers within Zoom without even having to have Photoshop installed or open.
In order for Zoom to properly read the layers in a Photoshop document, you MUST checkin the Photoshop asset using the Creative App Plugin in Photoshop CC or greater. The reason for this is that Zoom depends on Photoshop to read the information about the asset layers. It does not matter whether the asset is a new asset or a new revision of an asset already in Zoom; as long as the graphic is checked in using Photoshop, Zoom will read the layers.