I think you should read that as: "Which countries have laws which allow border inspectors to demand usernames/passwords to online services?" Those which do demand it are a subset of those which can demand it.

Your sovereignty argument is such an extreme interpretation of the question that it's almost certainly not what plg had in mind - if plg did have it in mind, then I find it hard to believe that question would have been asked in the first place.

Consider the question "what countries on border entry can draw and quarter entering citizens?" Your viewpoint seems to be that the correct answer is "all of them", yes?

Yes I was asking which countries are known to routinely demand login credentials for online services, and I don't mean who does it for a small number of persons-of-interest but I mean who does it routinely?

That would be hilarious:

Room Temperature IQ Goon (RTG): Give me your facebook password

Me: I don't know my facebook password

RTG: How do you login?

Me: I have a service to hold all my passwords

RTG: What is that service and what is the password

Me: Lastpass, but I don't have the second password

RTG: Second password?

Me: Yes, it requires me to use a U2F token to generate a second password

RTG: What is a U2F token and give it to me

Me: I leave it at home for security

RTG: Give me your phone

Me: Hands over 3310

RTG: Your real phone

Me: I don't travel internationally with a phone that have any data on it that I care about.

Of course the real solution is that I don't travel anywhere.

> All countries can demand it. They are sovereign.

"Sovereign" is a fancy word that boils down to, we have enough police- and/or military power at our disposal that we can force you to do it.