Where does your photos goes when you upload them
Where does the photos goes when you click upload
If you mean where is iCloud then there is no one answer. Apple has at least five massive data centers in the USA that I know of and all are integrated to produce what we all use as iCloud. The data center in NC is around a half a million square feet and has its own 200 acre solar power farm next to it. There are also Apple data centers in Connecticut, Nevada and California that I know of.
One of the huge advantages of cloud resources is they are highly redundant and never housed all in a single location. That protects against data loss as the system is so massively redundant, and separated by locations used, that no single point failure effects data.
In the past at least (and perhaps still) Apple also used resources of Amazon Web Service and Google web services, and other cloud providers for redundancy and excess capacity as needed. But they have spent many, many billions of dollars on their own data centers since iCloud was first available so I don’t know how much they rely on other cloud service providers these days.