Nbextension's require url is referenced by two different yaml files

I am trying to turn on an nbextension. I’m getting an error:

This nbextension's require url (codefolding/main) is referenced by two different yaml files on the server. This probably means that there are two installations of the same nbextension in different directories on the server. If they are different, only one will be loaded by the notebook, and this may prevent configuration from working correctly. Check the jupyter notebook server log for the paths of the relevant yaml files.

Where should I look for this server log?

I have installed Jupyter using Anaconda on Mac OS X

Can you run cmd jupyter nbextension list to show your nbextensions info?
And how do you enable a nbextension before?

Well, that doesn’t answer the question of where do I find the server log, but it does seem to answer the question of where the duplicates are.

Known nbextensions:
  config dir: /Local/Users/vlb/.jupyter/nbconfig
notebook section
  nbextensions_configurator/config_menu/main  enabled 
  - Validating: problems found:
    - require?  X nbextensions_configurator/config_menu/main
  contrib_nbextensions_help_item/main  enabled 
  - Validating: OK
  spellchecker/main  enabled 
  - Validating: OK
  execute_time/ExecuteTime  enabled 
  - Validating: OK
  snippets/main  enabled 
  - Validating: OK
  collapsible_headings/main  enabled 
  - Validating: OK
tree section
  nbextensions_configurator/tree_tab/main  enabled 
  - Validating: problems found:
    - require?  X nbextensions_configurator/tree_tab/main
  config dir: /Local/Users/vlb/anaconda3/etc/jupyter/nbconfig
notebook section
  jupyter-js-widgets/extension  enabled 
  - Validating: problems found:
    - require?  X jupyter-js-widgets/extension
  nbextensions_configurator/config_menu/main  enabled 
  - Validating: problems found:
    - require?  X nbextensions_configurator/config_menu/main
  contrib_nbextensions_help_item/main  enabled 
  - Validating: OK
tree section
  nbextensions_configurator/tree_tab/main  enabled 
  - Validating: problems found:
    - require?  X nbextensions_configurator/tree_tab/main
  config dir: /usr/local/etc/jupyter/nbconfig
notebook section
  nbextensions_configurator/config_menu/main  enabled 
  - Validating: problems found:
    - require?  X nbextensions_configurator/config_menu/main
  contrib_nbextensions_help_item/main  enabled 
  - Validating: OK
tree section
  nbextensions_configurator/tree_tab/main  enabled 
  - Validating: problems found:
    - require?  X nbextensions_configurator/tree_tab/main

And how do you enable a nbextension before?

I check the little box