Hello! I am going to make some assumptions. Please correct me if I'm wrong.
Since you are posting on the Network Analyst forum, I will assume that you want to get one of the NAClasses out of an NALayer. For example, you want to open a Closest Facility layer and access the Facilities as a feature class.
You already have a layer as an ILayer. Cast your ILayer as an INALayer.
var naLayer = layer as INALayer;
Via the context and NAClasses, get the naclass and cast it as a feature class.
var facilitiesFeatureClass = naLayer.Context.NAClasses.get_ItemByName("Facilities") as
IFeatureClass;Here is a code snippet that also works: