“How does “fair dealing” apply to playing music on my podcast? If I have a guest who says a song really affected him as a child and how he developed as an artist, can we listen to the song together and discuss it on air?”

As a general rule of thumb, if your use of the copyrighted work falls under more of a commercial purpose then it’s likely not going to be fair dealing. But if what you’re using the work for has more of an educational/research purpose – which is what it sounds like here – then fair dealing could apply. If you’re taking a critical lens to the work there are a couple of things you’ll need to have: the source of the work (where you got it from) and the name of the author/artist/performer/creator of the work.
If you’re really worried about if your work falls under fair dealing consider the following: what is the purpose of your use of the copyrighted work? (As above, is it commercial or education/satire/etc?) How did you use the song – is it going to be played multiple times throughout or just used one time? And is your podcast going to be widely distributed so that the copyrighted song will also be widely distributed? The less it is distributed or repeatedly used the less likely you’ll be in violation of copyright/fair dealing. How much of the song did you play? Was it just a minute of it or the whole song? The less of it used the more it falls under fair dealing. Were there alternatives to using the song? Was the song necessary for your podcast or could you have used something different? The nature of the work: is there a public interest in having the song in the podcast? And what was the effect of your use of the song on the work itself? Does it compete with the market of the song? (Case: CCH v LSUC)
The Queen’s Film & TV Research Group are not lawyers, and this is not legal advice! For more information on copyright law, please see the Copyright Law section of this site. Find out more about Queen’s Law on their website, and Pro Bono Queen’s at the PBSC Queen’s site.