Where are my bitcoins stored?

A bitcoin is nothing palpable, it's just an inscription in a big book of which there are thousands of copies (and no original).

Bitcoins are not stored at a specific location, but on all nodes in the network at a time, in the blockchain . So you can receive bitcoins even if your software wallet is off, or even if you have no wallet, but just a couple of cryptographic keys noted on a piece of paper. Software is only needed when you want to spend your bitcoins.

So the question is not where are your bitcoins, but where is the secret of your private key hidden ?

Whoever knows this key has the bitcoins associated with it.