Here is a link to a VEX engineering notebook you can purchase. Your coach should have gotten at least one copy of this notebook upon registering the first team for the year. The examples in the front of this book provide some useful guidance. (Click on “more views” in the link below to see a bit of what that looks like.) You are not required to use this notebook. As noted above, every organization which registers a team gets one complimentary notebook for the first team they register, so you don’t have to buy one to have access to the examples.
Here is the Judge Guide, which includes specific information about the Engineering Notebook. Page 9 has a description of what an Engineering Notebook should do. Page 15 has the Design Award Rubric.
Here is the Design Award Rubric in a separate document, which may be more convenient than the Judge Guide. Note that the first page is the specific rubric used by judges to evaluate the Engineering Notebook.
Here are several Q & A clarifications concerning the Engineering notebook, all answered by @Tarek Shraibati. He is the RECF authority on Engineering Notebooks.