What's the correct way of referencing nodes (for example textures) from another material builder subnetwork? Arnold has Fetch node to do that. I was looking for something similar for Karma to avoid duplicating shader parts.

I know V-Ray in Solaris provides a VOP node that does exactly what you're wanting, but I'm not sure if there is a native equivalent.

You can right-click > Actions > Create Reference Copy, but the channel references will be relative, not absolute. You'd need qLib tools to convert them from relative to absolute (which you will need when moving the shading node to another material builder or Material Library, otherwise the references will break).

https://qlab.github.io/qLib/ [qlab.github.io]

See here for more: https://forums.odforce.net/topic/47543-create-absolute-reference-copy-of-a-node-solved/ [forums.odforce.net]