If you are interested in the Where-used list of SAP objects, you need the report SAPRSEUB. This one is able to create the "where used list" for all SAP objects as well.
Normally, the "where used list" for SAP objects is only very limited filled. So, it is typically, that only about 20% of the data is filled. Therefore, the results are not very helpful.
When you want to have a complete overview on cross refereces of the SAP tables and ABAPs, you need to run SAPRSEUB. You should keep in mind, that this needs about 10 GB space in the DB and takes about 2 days to complete.
But then, you really have a perfect tool in order to understand the SAP sources in detail ;-))
More information on report SAPRSEUB is available in note 28022.