Does Executor of will usually produce all assests and where money came from? How do we know they not with holding an insurance policy or bank account

Your state, like mine, may require an Inventory to be filed with the court as a public document and let beneficiaries demand an accounting after a certain amount of time has passed.  However, a life insurance policy pays to the named beneficiary and is not part of the probate estate listed on the Inventory (or the Executor's responsibility).  A bank account may be pay-on-death or joint with right of survivorship.  If so, it, too, is not listed on the probate estate and is not the Executor's responsibility.