Okay, no problem. I will answer your question about how to get the path to the Routes sublayer in this thread, and I'll answer your travel mode question on your other post.
From what you've said, you don't actually need the feature dataset path specifically. You just need to retrieve the Routes sublayer of the Route layer and save it out to another feature class, right?
Check out the last code sample (called "MakeRouteAnalysisLayer example 4") on this documentation page:
Make Route Analysis Layer (Network Analyst)—ArcGIS Pro | Documentation
I think that demonstrates exactly what you're trying to do. Essentially you need to use the .listLayers() command on the Route layer object to retrieve the Routes sublayer object, and you can use that as input to other geoprocessing tools, like CopyFeatures.