Too bad... it would make it easy if the SKU for the product with attribute could be built from base product SKU + attribute SKU fragment.

Each option name and each option value has its own id, and when one of these values is applied to a particular product, it acquires its own unique attribute id (which would be stored in the db, keyed to product, option name and option value). You could add a new field to that table for attribute_sku, and the required code to insert it from admin and retrieve it for display/use.

Inserting would probably best be done in the Attributes Controller.