If no designated beneficiary of life insurance was specifically identified by the deceased, the amount payable under a life insurance policy will be part of the assets to be listed in the inventory of the succession/estate.
Before being able to proceed with the estate inventory of the deceased's assets and to know the relevant information about that, you will have to check with any insurance company with whom the deceased would likely have held a life insurance policy.
The letter requesting information from an insurance company, available in multiple formats on this website, will be suitable for most situations.