Yes, the coil sticking out of the back is the field winding. This is not a permanent magnet motor as you might find on 1950s HO scale trains or even 2-rail O scale from that era. The field is energized by current flowing through it, in series with the armature. The motor will run on AC or DC. Most postwar operators use a Lionel transformer designed for 50-60Hz AC.
For test purposes, you could attach one transformer lead to one brush, and the other transformer lead to one side of the field. But in order to make it run you also need a third connection between the other brush and other side of the field. So you will need 3 leads with alligator clips to test it.
To recap, the series circuit goes: Transformer -> Brush 1 -> through the armature (one winding at a time depending on commutator phase) -> Brush 2 -> Field 1 -> through the field -> Field 2 -> back to transformer. It doesn't matter which brush or which side of the field is '1' or '2'.
To use the loco for operations, you'll probably want to add the mysterious "E-unit" into the circuit. This is a cyclical sequencing switch that changes the polarity of the brushes relative to the field. This causes the motor to rotate in the opposite direction. Hope this clears things up, can't wait to see it run!
