Just looking for some advice around APIs

Nikv - If online help articles are not part of LITHIUM, there are two approach to achieve this. 

Approach 1 :  Custom Search

Create a new component for search. You will need to hit both query at the same time and need to find a way to combine the result of both query. 

Query 1: Get messages from lithium.

For the lithium you can use the below query. 

SELECT * FROM messages WHERE subject MATCHES 'wireless' OR body MATCHES 'wireless'

You can find the reference here https://community.lithium.com/t5/Developer-Documentation/bd-p/dev-doc-portal?section=commv2&collection=messages#constraints-subject. 

Query 2 :  Get all the matching article from online help article server. 

Second Approach : Open Source Search Platform 

You can built your search using open source platform Solr and Elastic search. 

Here is the documentation for both. 

http://lucene.apache.org/solr/

https://www.elastic.co/

These platform store the data from different platform and combined them so you can get the result with only  single query. 

Here is the example of Solr search which we have done for Optmizely community. 

https://community.optimizely.com/t5/forums/searchpage?q=search&pnum=0&refineType=

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Tariq