You need every tool in your arsenal, because there are several different training needs:
UNIVERSAL NAVIGATION
How the navigator bar works. Navbar shortcuts. List view manipulation. Workspace navigation. All the stuff that would be exactly the same in every ServiceNow instance. I wouldn't reinvent the wheel here, I'd just pack a KB article with existing Youtube videos like these.
PROCESS SPECIFIC TRAINING
This is way harder to outsource since you're either modifying OOB stuff or building your own new process apps. But here you need two critical components.
1) How does XYZ Process Work: Navigation and process is NOT the same thing.
2) How do I execute XYZ Process in ServiceNow: This is where navigation and step-by-step guides come in. When I was freelancing I'd build "Playbooks" for the processes I deployed. Think of this less like a description of features, but more like football plays. The information is indexed by the play... the thing you're doing. Like in SPM the index might be...
- How do I propose new work?
- How do I evaluate a demand?
- How do I create a project from a demand?
- How do I add risks and issues to a project?
- How do I baselines a project?
- etc etc
REPORTING
No matter what the process is, someone's got to report on it. Remember that it isn't your users' jobs to be expert ServiceNow resources. You can never underestimate how much help people need here. I would build a library of videos either internally or externally. Remember that the point is enablement... not necessarily creating the content yourself. You'll just be a curator.
Here's one of my reporting playlists to get you started
https://www.youtube.com/playlist?list=PLkQDoKoP0MANyQVOGxtP5zChkVpFqMibd
