Make sure that CoqIDE (8.6 or newer) is installed and coqidetop or coqidetop.opt (coqtop for Coq versions before 8.9.0) is in your PATH. Also, make sure the python command is recognized on your machine. If not you can set up an alias for it e.g. python-is-python3 on Ubuntu. There are a number of convenience improvements over standard Jupyter notebook behavior that are implemented to support Coq-specific use cases.