The scaffold command is a built in command that is available across all Odoo versions.
Usually you should execute the Odoo main file, which is usually named odoo-server. For example in V11:
./odoo-bin scaffold your_module_name addons/
In V10 and below:
./openerp-server scaffold your_module_name addons/
You can find more information and details in the official wiki about this too! See https://www.odoo.com/documentation/11.0/howtos/backend.html#module-structure
Please try this in your terminal for v10 and v11:
python odoo-bin scaffold new_module_name