tsql to find users and database level permissions mapped to a certificate
You can use this table to find users mapped to certificate

select * from sys.database_principals where type = 'C'


If the principals are SQL users, maybe you will have to remap users because when you migrate users and logins from one sql server to an other, SID aren't regenerated and may be different on the new server. So all the link on the users aren't valid.

Hope this help you.