SAP

If you are planning to work in a manufacturing firm, SAP Production Planning (PP) module will be a good option for you. SAP PP is designed specifically for production planning and management. SAP PP module collaborate with master data, sales and operations planning, distribution resource planning, material requirements planning, Kanban, product cost planning and so on while working towards production management in enterprises.
If you are planning to work in logistics or SCM functions then SAP Materials Management (MM) will be a good option. SAP MM module manages materials required, processed and produced in enterprises. Sub-components in SAP MM module are vendor master data, consumption based planning, purchasing, inventory management, invoice verification and so on.
Certification on SAP PP and MM together is very good options for all engineers in core branches of engineering.

SAP is the world's largest selling Enterprise Resources Planning (ERP) software system. For implementation of SAP, you require ABAB developers and functional consultants. If you want to make career in Technical, you may learn ABAB and do certifications. In case you want to be a functional specialist, you can do one of more functional module certification. SAP professionals are paid above normal developers and Business Analysts. With SAP certifications, you can join IT companies or IT department of business enterprises. As you have sales and marketing experience, you can start your SAP career with certification in Sales & Distribution (SD) module of SAP.