https://github.com/googlesamples/assistant-sdk-python/issues/236#issuecomment-383039470

You are trying to install the package to a system folder which you don't have permissions to write to.
You have three options(use only one of them):
1-setup a virtual env to install the package (recommended):

python3 -m venv env
source ./env/bin/activate 
python -m pip install google-assistant-sdk[samples]

2-Install the package to the user folder:
python -m pip install --user google-assistant-sdk[samples]

3-use sudo to install to the system folder (not recommended)
sudo python -m pip install google-assistant-sdk[samples]