As far as i know, you are supposed to pay some sort of tax for "money brought to the country". This can only occur if you use a State approved exchange. I doubt many people use those, there is no need unless you want to get rid of Petros...

Because ATMs are physical, i suppose they are prone to State control. I don't see myself ever using one...

How exactly can you enforce Bitcoin taxation? Force people declare what their wallets are? What stops them from having hidden (undeclared) wallets?

Bitcoin is nowhere physically, and everywhere. It lives on each node, which there are several across the globe. It is not really crossing borders, and yet reaches everywhere. The old thinking just doesn't apply here.

Since its not really "in your jurisdiction", how exactly do you intend to enforce your laws to it?

Only way i can see some taxation going is, for example VAT. At purchase at a shop, and even there could be undeclared (hidden) wallets. Similar to people wanting to avoid taxation, they could forge the accounting book, etc. It would need to be investigated, which you can do a (physical) shop. And then you would also need to make sure your tax collectors are honest, and at the end you have a police state that can never ensure everyone is paying their taxes, but spend a lot trying to make sure they do (If only that money was used elsewhere...).