There are various bodies involved in the certification of the different elements involved in GSMA compliant eUICC applications.
The GSMA operate a scheme called Security Accreditation Scheme ( SAS ) that provides a certification of the site belonging to an organisation that provides Remote SIM Provisioning services. Details of the scheme and a list of approved sites is available on their website.
GlobalPlatform tests and lists the actual certified eUICC chips on their website. Select “eUICC” from the drop-down to see the eUICCs that are currently approved.
The GSMA implements a trusted system through the use of signed root certificates.