Hi Maria,
Not sure i fully understand what exactly you’re trying to achieve but here’s what should be possible:
You can search over metadata model in ONE, that should allow you to identify the relationships between different entities. You can find it under Global Settings → Metadata Model → Model Graph. However it is mostly used to understand how different entities are related if you want to export some metadata from the platform.
As you mentioned is possible to search over instances of specific entity (rules, catalog items, components, etc.) using names, often you can use some filters or AQL, but you can not search over the content of the rules or components.
You can search the xml code of specific component by opening them in ONE Desktop application as text files.

In general all the search options are described below:
https://docs.ataccama.com/one/latest/common-actions/search.html
AQL:
https://docs.ataccama.com/one/latest/common-actions/aql-expressions.html#overview

I hope this answers your question.

Ivan