Let's see by parts:
- To become an ISO 27001 trainer you have to select a training provider you want to work for and follow its rules regarding how to become a certified trainer.
- To become an ISO 27001 Auditor you have to attend an accredited course. To become an internal auditor you only have to finish the course. To become a Lead Auditor (a more interesting path for a career in ISO 27001), you also have to be approved on a final exam. To become certified, besides passing the exam you also have to perform some audits for a certification body.
- To become an ISO 27001 Lead Implementer, you have to attend an accredited course, and be approved on a final exam.
The best pathway will depend on your professional objectives. If you plan to work on an Information Security Management System certification process, then you should consid er the Lead Implementer certification. If you plan to ensure the operation of an ISMS, then you should consider the Lead Auditor certification. The training path should be considered if your purpose is to use your knowledge and experience to help other in ISO 27001 career.