The GDPR also requires that any Consent given must be understood by the subject regardless of their age, education, or human language issues. Thus any organization gathering data must provide various forms of their consent language that can be proven to be understood by that patient. The FHIR Consent supports this by having a place to record the actual text presented to the patient. Clearly deriving that text originally is not a FHIR issue. It is a very difficult task, and I feel for small organizations. Similar capability to record the actual text presented to the patient is also available in IHE BPPC which supports APPC for this purpose.
As with any Privacy regulation one must have good Provenance proof of where all data came from, including when it was imported from the Patient themselves. One must also have good AuditEvent records to show where and why the data was used.