Air carrier First Officer reported experiencing GPS jamming departing RKSI/ICN airport. GPS functionality was eventually regained.

Narrative

On the EGOBA 2E SID at around 8;000 feet. Relief Pilot seated behind the flying First Officer.Climbing out of 8000 feet the crew started to note the effects of being jammed as they were between EG070 and EG140 and onwards. NAV Unable RNP & ADS-B Out Left and then Right Illuminated on the EICAS Message. ANP shot up to 20.0 miles. At Captain's; request; the Relief Pilot seated behind the Flying First Officer began running the GPS interference or spoofing procedure.Once the Procedure was completed the Captain requested the Relief Pilot to help call Dispatch. Satcom was not ringing or could not broadcast. Relief Pilot seated behind the flying First Officer switched seats and started switched the Satcom to Sat-IR Iridium and tried to place call which was unsuccessful. Then the Relief Pilot switched radios back to regular SAT and placed a call which received an answer. Dispatcher noted that there was a shift change. Then the Relief Pilot requested if Maintenance Control was able to get on the line. The process took a while because Dispatcher had difficulty patching Maintenance Control into the call.Meanwhile; the Relief Pilot queried the Dispatcher if there were any new NOTAMs or alerts for the area of flight which was not directly or promptly answered. Once Maintenance Control was on the line; there was a bit of difficulty initially relaying what was going on advisory-message wise. The crew wanted to know when and if they could turn back on the GPS procedure which there was not much guidance by Dispatch or Maintenance Control.Meanwhile; the Relief Pilot noted that the RAD NAV INHIBIT portion of the GPS spoofing procedure was not actually turned to off which explained more the delay of the ANP returning to functionality.Eventually; the Crew decided to follow the clear of interference portion of the GPS interference procedure. At this time; ANP returned to normal and the GPS started updating as usual.