I agree with Bastien regarding the initial setup and structure of your organization. Nice work!
I also really like his consideration for this use case to take advantage of a recent post about reporting on at-mentions. You can find it here:
I’d recommend that your at-mention of the document be in the comment field of the task. That way it can’t be deleted by users and thus the reporting of this at-mention will remain intact.
Within your Master Resource you could list all the various reports that capture tasks being completed by employees through onboarding. This would be really helpful for the reporting managers to see what topic-based items their people have taken action on.