Hi.
You're right. This node is call "Peg Bar" and works similar as a empty layer in After Effetcs.
To add it, first, in Schematic switch to the Stage mode and you will see the adding Pegbars button in the right-bottom section panel.
Once you add the pegbar, you can animate it and add new nodes to this one.
Now, something very important: in OpenToonz, pegbars only can be linked to the table.
Best!