First, there are two purposes for tracing requirements. 

1. One is allocating requirements within the scope of a projects. It would answer a questions like, "Do these solutions requirements meet all the stakeholder and business requirements?"
2. The other is is creating relationships between things to assess impact. This may not be during a project, it may be at enterprise analysis. It answers a question like, "I want to change this aspect of the system, what are all the impacted processes, business rules, functions, etc" 

The Good: In Document Requirements Tracebility

If you working in your standard Word document you start with your high level required capabilites at the top of the document, you can either list each requirement that relates to it that exist in the sub requirements or you can list the related high level requirements within the sub-level requirements 

The Better: Excel Requirements Tracebility

One way to trace requirements, is by creating a requirements traceability matrix in excel. This would be most likely be used to determine if maybe every solution requirement is aligned to a design specification. See excel requirements traceability matrix example

The Best: Requirements Management Tool Traceability

Requirements management tools not only give you the ability to create relationships on the fly. You could trace busines requirements to solution requirements, to business rules, to business process, etc. Then some time after the fact you can create reports that are actually valuable to someone and can be used to make informed decision about your solution. See business requirements tool requirements traceability matrix example

Good luck with your future tracing and please share any other recommendations for requirements traceability management