Who can be named representative under article 27 of the GDPR
The GDPR only requires that the representative is established in a Member State where the data subjects whose personal data is processed are. If you process or may process personal data from any data subject within the EU, you may appoint it in any Member State.
Notwithstanding the above, in those cases where you process personal data of individuals of more than one Member State and most of them reside in one specific State, good practice highlighted by the EDPB on the Opinion 3/2018 on the territorial scope of the GDPR (version for public consultation) is to designate a representative which is established in that same Member State where most of data subjects are.
The gdpr representative may be an external, natural or legal person, but also a subsidiary. Where the representative is a company or organisation, it is recommended that they assign a single individual as lead contact and person in charge.