Finding out which country has the most Bitcoin's is not something that you can easily calculate it is very difficult as it involves geolocating the IP addresses. But with the way they get transferred it could be very different the next day. Also a lot of Bitcoin users are concerned about privacy and security and it may be difficult to acquire the actual geolocation data.
On the other hand.I can give you the numbers for Top five countries for Bitcoin downloads as of Today
1.US (1,207,661)
2.China (505,904)
3.Germany (270,043)
4.UK (236,523)
5.Russia (226,680)
Hope this helps
Can you define what you mean? Is this about governments or central banks posessing bitcoins? Or about their citizens? The best bet to find an answer could be geolocating the IP addresses seen relaying transactions, but I do not know if it even possible to distinguish between the originator and a relayer... – pyramids – 2013-11-28T16:06:15.567
@pyramids the vast majority of Blockchain.info data says the middle of the ocean, ie unknown location 0N 0W – Wizard Of Ozzie – 2014-10-13T09:22:38.173
What is your definition of a bitcoin being held by country X? If there are 10 bitcoins on a 2-of-3 multisig address, and the three people holding the keys are in France, Italy and Spain, and the wallet is actually stored on a computer in England and a copy is in the cloud on a server hosted in Iceland.. What country holds the 10 bitcoins? – Madzi Konjo – 2014-11-12T00:55:07.690