If you need to get the python path used by plpython you can create a new function that prints out the system paths.

To get started, create a function called python_path or whatever you want to call it:

CREATE FUNCTION python_path ()
    RETURNS text[]
AS $$
    import sys
    return [p for p in sys.path]
$$ LANGUAGE plpython3u;

Now you can list the paths by running a select query with the function:

SELECT UNNEST(python_path());

For me the output looks like this: