Auditing company manufacturing wood and plastic products

Answer:
In my answer, I will just focus on what is specific of that manufacturing company: wood and plastic products.
I would consider the life cycle of those materials. Does the wood come from certified forests? Does the wood include recycled wood? Does recycled wood come from operators with a permit? Does the organization buy recycled plastic? Does recycled plastic come from operators with a permit? Does the organization reuse plastic and wood?

The same exercise can be made based on the environmental assessment of aspects and impacts and risks and opportunities, and on the legislation and regulation applicable.

The following material will provide you information about the assessment of environmental interactions and internal audits:
ISO 14001 – 4 steps in identification and evaluation of environmental aspects - https://advisera.com/14001academy/blog/2019/08/27/key-iso-14001-benefits-to-customers/ nowledgebase/4-steps-in-identification-and-evaluation-of-environmental-aspects/
How to make an ISO 14001 internal audit checklist - https://advisera.com/14001academy/blog/2016/06/27/how-to-make-an-iso-14001-internal-audit-checklist/
Free online training ISO 14001:2015 Internal Auditor Course - https://advisera.com/training/iso-14001-internal-auditor-course/
Book - THE ISO 14001:2015 COMPANION – A Straightforward Guide to Implementing an EMS in a Small Business - https://advisera.com/books/the-iso-14001-2015-companion/