The original file that was uploaded will likely have its file name stored on the 'name' or 'res_name' of the ir.attachment model.

When a file is uploaded to Odoo it gets stored in the file store or in the DB as just binary data.

In the DB its stored in a binary field. On the file store , its saved in an indexed folder with the file name being a unique id.(Not the original file name as there could be multiple files with the same name)