What's the simplest, open, animation format?
For what it's worth, the glTF Tutorials contain a section on Skinning that shows how the raw vertex and joint weight data feed into a vertex shader to distort the mesh.
If you do design your own format to hold this, you'll need tooling to export it from 3D content creation software, as well as software to read the new format into your application.  Using an open format like glTF can grant access to existing tools, such as the Blender glTF exporter, that can write all this data into the file, in a form that's ready to load into vertex attributes and shaders.