I have found CitationQueryEngine - which

There is also this
https://llamahub.ai/l/llama-packs/llama-index-packs-fuzzy-citation?from=

Which uses fuzzy-matching to indentify which sentences in response.source_nodes were used to write the response

(response.source_nodes already contains all the nodes sent to the LLM to generate a specific resposne)

The code is pretty basic, it just post-processes the response object

Thank you