A second officer is usually a flight engineer, and as such will log flight engineer time only. As well, with most 3-seat aircraft going away, there is probably not a long term career option for someone just getting into that job. It is not a piloting job at all, and is not looked at as such by hiring airlines. However, historically speaking, the flight engineer job at most airlines was/is the entry level position, from which guys progress, seniority permitting, from there through the first officer (co-pilot) seat to the left seat. Good luck.