Where would I find out where to pick up the shuttle bus to Washington park

If you arrive by subway, right outside you'll see the entrance to the zoo and a stop of the purple shuttles.

The Free Washington Park Shuttle runs year-round. May-Oct it is every day, Nov- march the shuttle runs on weekends only. There are a handful of spots but the main three are right outside the Max station elevator nearest the zoo, Hoyt Arboretum and one between Portland Japanese Garen and the Rose Garden.