Just for stats I want to know which nation has its dominance or maximum user on physics.stackexhange.
There is a limited amount of site analytics available to high-rep users but this does not include any geographical information. Geographical data on visitors (not users) is presumably available to the SE team but it is not made available through that channel; you'd have to ask the SE team directly to get it.
Self-declared user location data is available through the Data Explorer, but as e.g. this query shows, being user-provided it is a huge mixed bag and you'd need some processing to make statistical sense of it. This query makes things a bit easier to handle, and the corresponding code described here can help draw some inferences if that's where you're headed.
On a similar track, StackMaps can help provide a geographical view (but not quite a statistical one) on this information.
Generally, though, this information is hard to come by and to handle. Visitor geographic data is not available, and user geographic data is self-reported, so for one you should take its accuracy with a grain of salt, and there is an enormous selection bias you need to take into account: 48k of 105k users have not provided any location, and some fraction have provided fictional location. Moreover, it is at least likely that whether a user reports their location is correlated with the location itself (so users from e.g. Africa might feel that declaring their location is not advantageous, so that location gets (severely?) under-represented in the self-reported data).