Re: If you are going to be a cybersecurity advisor ...
Very sound advice from @CISOScott
I often find the best way to validate my own knowledge is when I attempt to teach or indeed participate in discussions/consultations. I also find that the knowledge I lack or things I have forgotten often get pointed out by those being taught or indeed those I have conversations with.
It's always best to be honest, say that you can't recall or indeed do not know, research the topic (or refresh on it) and go back to the person who was kind enough to point out your shortcomings.
But going back to the original post, I would agree with @rslade. If you don't know what you are preaching about, don't preach. It will only lead to some sort of issue, either for you or the intended recipient.