It is not necessary to establish a system that can’t be cheated or dodged. No system is that tight but the first move needs to be put in place controls on expatriations of capital or currency. Some countries already do this. Wealth generated overseas will need special treatment.
How do we know if someone “accurately” reported their wealth?
Just like we do now in regards to income, we audit them randomly and due to suspicion. Any wealth not reported is subject to confiscation. You don’t claim it, it is not yours, it is now ours.
What if it’s owned by a trust or family limited partnership or an offshore corporation with no ties to the United States?
No ties to the U.S. then it is not taxed. Trusts with U.S. beneficiaries, the beneficiaries need to report that wealth, same for limited partnership. U.S. residents and citizens wealth would be taxed not Foreigners.
The property might be here, but the legal right to its ownership is beyond the reach of the U.S. government. What will you do then?
Nothing, if the owner is not a U.S. resident it is not taxed. We are not taxing the world to pay our bill just U.S. residents and citizens. If a person chooses to renounce there U.S. citizenship their wealth would be noted at that time and that wealth would be taxed in perpetuity and would continue to be under currency and capital controls to limit expatriation.
How will you “confiscate” wealth whose ownership is outside of U.S. jurisdiction.
We don’t, if the ownership is a U.S. resident/citizen then they are in U.S. jurisdiction. If they are in a foreign country most times extradition is an option and failure to repatriate funds to allow confiscation in violation of a court order could result in penalties including prison time.