They come in two varieties:
FEs- Non-pilots that are certificated as FEs only and man the FE seat permanently. Known in the biz as PFEs, or Professional FEs. Only ones remaining of these are in the cargo world, that I know of. Having a pilot license not required, since most PFEs are prior A&P mechanics that move up to become cockpit crewmembers in the FE seat.
Second Officers- Flight crewmember at a cargo/pax airline that is a pilot, but becomes FE certificated to man the FE panel as a new-hire, prior to advancing to co-pilot or aircraft commander. Not many of these remaining in the pax world due to few planes in service these days that have a 3-member cockpit crew.
Formal training incorporates primarily a systems knowlege-type course for the each of the three FE categories that one is training for: FE-turbojet, FE-turbopropeller, and FE-reciprocating.
Doug would be the primo-man to answer any more detailed questions due to his holding a FE-turbojet certificate, and being a former second-officer himself.