You need one management license for each Jamboard
You can buy a license annually — either directly from Google or your reseller. Licenses cost USD 600 per year.
Purchase and activate Jamboard licenses on your primary domain, not on secondary or alias domains. If you have more than one Jamboard in your domain, the licenses are transferable among them. If you return one board, you can use an existing license in your domain for the new board you receive.