The annotate window has a very clear separation between an assessor's and the contributions of any co-assessors to an assessment of a paper. Annotations and comments need to be shared before they are accessible to others. They are, by default, set to private, but this can be set otherwise on the whole license.
If the co-assessor has shared any annotations or general comments with the assessor, he/she will be able to access these in the Summary:
With the Filter button, you can choose what you want to see in your summary and with the Print button you can export the summary as a PDF-file: