The same plugin used - Rest API for Obsidian, can also query your notes. This enables you to use the HTTP node in n8n, which will make a GET request to Obsidian, fetch the text, then output it to the vector database I mentioned earlier. This usually is only required once, if you use a vector db like Pinecone, which will then stay online and wait to be queried by the AI Agent.
Obsidian API methods: Local Rest API for Obsidian: Interactive API Documentation
So, the approach is very similar, just the request you make will be different. But you will still need hands on experience in actually building this workflow with the AI + the vector DB (RAG) so you are confident in using it and also extending it as needed in the future 
I recommend checking out the starter template and any other tutorials on that. If you need help with the HTTP node and making the requests to Obsidian, we will also be happy to help!