B767 Relief Pilot reported encountering wake turbulence and during the event the FO EFI failed; leading the flight crew to divert.

Narrative

Before our departure to ZZZZ; our inbound aircraft had the CA Electronic Flight Instrument (EFI) written up. It had to be used in ALTN mode; so the CA symbol generator was deferred. The C and FO symbol generators had no known issues. Since we had 2 working symbol generators; we elected to accept the aircraft and to depart after a conversation with Maintenance Control. I was the Relief Pilot on this flight; and I had the first break. While I was preparing to go back to the flight deck during the last few minutes of my break; the aircraft encountered wake turbulence. I had to remain seated until the wake turbulence subsided before we would start our crew change. When I was able to enter the flight deck; the CA informed me that during the wake turbulence event; the FO EFI failed and that it was currently in the ALTN mode. They were currently talking to our Dispatcher and Maintenance Control at the time. We had started to coast out when this happened. As a crew; we discussed whether or not to continue with the crossing with only one symbol generator working; or to turn around and head towards EWR. We elected to contact ATC to get a reroute to turn towards EWR. After receiving our reroute; the flight attendants and passengers were informed about the situation and our plan to return to EWR. The weather between our present position and EWR was VFR; and the arrival and the approach to landing were uneventful.