It's going to vary from program to program for sure. Technically anything that's part of the core curriculum from a CAMPEP graduate program is fair game, but it's not a comprehensive exam. Often with technical questions they're trying to assess how well you can explain technical details, or how you work your way through a challenging problem, rather than rote knowledge of a topic.
You can most likely expect to explain something technical in relatively broad strokes. Examples might include how a given detector works (ion chamber, OSLD, flat panel imager, gel dosimetry, etc.), how radiation kills cancer cells, or how Monte Carlo dose calculations are performed. I'd also be ready to summarize your MSc or PhD project.
You could also expect questions that explore or influence common phenomena. Examples include, what does a percentage depth dose curve looks like, why is it shaped like that, and what factors might change it? Or what factors influence how cells respond to radiation? Or a scenario where your morning output measurement has changed, what factors might have influenced this?