You. Should. Know. EVERYTHING!!!!!!!
naw. just b sure to openly state how much or how little u know about the subject beforehand and dont try to present opinion as fact like alotta republicans b doin nowadays.
There is no way of knowing everything about a subject/topic in this world where things change in seconds. As far as podcasts go, it would depend on the actual purpose the podcast is trying to serve. As long as you aren't trying to be a completely objective unbiased media meant to inform, then no. Illustrating your view and conveying the actual point you are trying to make will be more. Your perspective, which contains different experiences or trains of thought, is why people are listening. Anybody who truly wants in depth knowledge will seek that on their own. Plus everything ain't that serious or interesting enough to have to know all of it.
The whole thing about a podcast is the same with any medium. There is something being conveyed to another as in any conversation. It could be projected as informational, entertainment, both, or any context the provider is wanting to put out there. All conversations are catalysts in their own right. I know a lot about something, but in the group we have on our podcast, we interact and get to some points where we DO NOT know everything about the subject. We know what we experience, what we hear from others, and other means of sources which we consume. The exchange is the fun part. we learn, we deduce, and we have fun all the while.
Some folks take themselves way too seriously, but there should be a baseline of reason and intellect. Everything else is fluid and open. Not to mention building an audience goes hand in hand with delivery. If the content and delivery is compelling and/or entertaining, the audience will come.