To calculate A/R special charges, you must run the Aging Report (RAG) with Update Option S, "Calculate Special Charges," prior to running your monthly statements. You must also select Update Option F (finalize) to post the special charges to accounts. The special charges are created as "F" type documents, which you can access in Open Item Maintenance.
If you want to view the calculated special charges before you post them to your A/R accounts, run a non-final RAG (without Update Option F) before the RAG with Update Option F runs. To do this, run the first RAG with Update Option S, but without Update Option F, then run the second RAG with Update Options S and F.
You can run the RAG report(s) manually, or you can add the report(s) to your monthly queue. In fact, you probably already have RAG running in a queue at month-end. If so, you could simply modify the RAG in the queue so that it runs with Update Options S and F, in addition to the other options you use.