ok sorry what i meant was by int or ext is:
The keywords they want to track do they come from an internal search engine like: SOLR? basically any search that is based from a local search on website perspective.
The external is literally from keywords used by users from Google and bing that referred users to your website...
If its the first point then you need to create tags and events on your internal search results page to measure various search related metrics.
If its from the second point then you will face a challenge as much of the external keywords are hidden to Adobe analytics. Google encrypts most of the results. Hence your best bet for extenal keyword search data is to access Google or Bing search consoles...
I recommend you get your client to setup console for their domain at least in Google.
GLTU