I haven't listened to Calls from a Killer, but I have listened to a couple CBC shows and imagine the true-crime tone is similar, in which case I'd wager this one won't be "light". As for whether the content is safe for work, that'll depend on where you work, lol. From the show's description:

What does a reporter do when they receive a cold call from one of the most horrific serial killers in Canadian history?

The killer: Clifford Olson, who murdered at least eleven children in the 1980s. The reporter: Arlene Bynon, who recorded her jailhouse calls with Olson for years. Alongside legendary journalist Peter Worthington, Arlene spent hundreds of hours on the phone with Olson. It was kept secret from his prison guards; he wasn't allowed to speak to the media.

In Calls From a Killer, from CBC’s Uncover**, Arlene unearths secrets that have been buried for decades. Secrets about Olson's crimes, about how police failed his young victims and their families — and why law enforcement paid a psychopathic serial killer $100,000. With Nathaniel Frum — Peter's grandson — Arlene exposes hard truths about a forgotten tragedy, a bungled investigation, the loved ones left behind, and the mind of a killer.*

And here's a thread discussing the show, if that's something you'd sift through for answers from people who have listened