If you are alive, you have some gnosis of what you have experienced and observed.
If you are practicing gnosis daily, then you have gnosis from your comprehension of yourself, nature, the psyche, etc. You know how things work for you.
Start with this. Talk from your own experience. Keep to facts.
When you have to talk about things outside of your experience, be honest, but also rely on proven, reliable sources as support.
Yet, above all of this, the most important ethic is to be cognizant of the one who is hearing your words. Our words can heal and they can also kill. To know when to talk is as important as knowing what to say.