Auditing the Plant Manager

Answer:
I would concentrate on the interactions of the Plant with the environment:

What are the significant environmental impacts?
What is planned to control or improve those impacts?
Are those action plans being followed?
Are those action plans being effective?
Are procedures and or practices being followed?
Are potential emergency situations being prevented? Are there procedures for answering to those emergency situations? Were those procedures tested?
Is environmental performance improving?

The following material will provide you information about the assessment of environmental interactions:
- Defining and implementing operational control in ISO 14001:2015 - https://advisera.com/14001academy/blog/2016/04/11/defining-and-implementing-operational-control-in-iso-140012015/140012015/
- Internal Audits in the EMS: Five Main Steps - https://advisera.com/14001academy/blog/2019/08/27/key-iso-14001-benefits-to-customers/nowledgebase/internal-audits-in-the-ems-five-main-steps/
- Free online training ISO 14 001:2015 Foundations Course - https://advisera.com/training/iso-14001-internal-auditor-course/
- Book - THE ISO 14001:2015 COMPANION – A A Straightforward Guide to Implementing an EMS in a Small Business - https://advisera.com/books/the-iso-14001-2015-companion/