Sovereignty in 21st century terms IMO includes:
Military (having your own military - defence capability, both in manpower and tech/weapons)
Legislative: The ability to pass you own laws by political bodies where your citizens views are represented.
Economic, taxation and monetary policy: Having your own tax system, tax authorities, your own currency and the ability to have your own exchange rate policy.
It is my opinion that in 21st systemics, ie the role of China, the US, India, Russia, only a united Europe can provide such sovereignty instead of individual countries. The same way that city-states evolved to nation-states, the polities of the 21st century seem to need to have bigger size (in population, surface, etc) in order to achieve the economies of scale needed for sovereignty that is viable and can be maintained.
These are some of the areas sovereignty is need in our era, and this applied to the EU too:
1) Self-reliance in energy
2) A high level of self-reliance in at least staple foods
Food for thought:
In our era, does a state, and in particular the EU, need sovereignty in Finance?
Or at least at Eurozone level?
Sovereignty not only vis-a-vis other states but the global financial system as well?