If you are referring to an MMSI number then it will be on your ships radio licence. If that is too old to have MMSI then you will need to log on to update your license details and request a new one. All done online, takes 5 minutes. Then program DSC with the MMSI.
in the usa, the mmsi number is issued by gov by 'fcc' or issued by 'boat us' and the number is lic to the radio and boat combination. hope this helps or is what you were asking.
be careful programming your numbers, a mistake may require sending back to the maker to be corrected....care must be taken, read instructions before attempting.