In general, there are 2 main classes of SAP skills: functional and technical. Functional is more of a combination m of business and IT skills, while technical is purely IT skills.
By saying the SAP module, the majority will refer to the functional skills, especially the functional area in SAP ERP software, such as materials management (MM), production planning (PP), sales and distribution (SD), etc.
If you want to cross and enrich your skillset with business or functional skills, then considering your background, I would recommend you to go for sales and distribution (SD) or customer relationship management (CRM). Note that SAP CRM isn't a part of SAP ERP, it's a different product.
If you want to stay technical, the options are varied and some of SAP latest innovations fall on this category. You can opt for, whether you want to specialize in role or product/technology:
Role oriented (typical role in current SAP projects):
- SAP Basis (SAP administration and authorization management)
- SAP ABAP (programming)
- SAP HANA (in-memory database technology)
- SAP Business Objects (business intelligence)
- SAP Mobile Platform (mobility)
- SAP Fiori (user experience)
- SAP Lumira (analytics/visual intelligence)
To know more about these SAP courses one can join certification training of their choice.