I am curious to know how they would know?
There's a few series of border control related shows. They show the depths of idiocy people willingly engage in. Like
a guy who pretended to be a minor when he was clearly in his 20s-30s.
And specially how they can get the proof of it since the onus is on them to prove that the protected person/refugee had voluntarily reavailed themself of the protection of their country of nationality.
False. The onus on them is to prove that you committed an act that could be seen as voluntarily reavailing yourself of the protection of your country of nationality. It's up to the Member to determine whether or not this actually happened... and if you find yourself in this situation, I cannot recommend collecting evidence of how involuntary this travel was enough.
An example: If I were travelling from Seoul back to Canada... but my flight gets cancelled and they want to rebook me onto a flight connecting through my home country, my evidence for the involuntary nature of my travel to my home country would be a letter from the airline explaining what occurred, a print out of the original itinerary, etc. I would try to do my best to pre-empt and diffuse the case against me to show that I tried my level best to avoid it.
Do people share this information while renewing PR cards, or disclosing it to CBSA when entering the country after that action? Or how?
Not just this but the CBSA asking questions to try to reveal these answers. This is why I recommend knowing a good immigration attorney.
I can't imagine that all countries share the entry/exit information with Canada specially the travel document details (maybe name, dob only) so how would IRB know that this person used their national passport instead of RTD?
Because CBSA and/or IRCC could make an application for cessation of protection to the IRB. That's how the IRB knows. And CBSA officers are trained to ask these kinds of questions.