How can you tell which of the theaters or movies at regal union square are 4dx; that is, have motion chairs, etc.? (I'm trying to avoid them.)

auditorium 5 is 4DX at Regal Union Square. & before you purchase tickets for films via the app. it will let you know, with the showtimes, what films are 4DX or ScreenX, or standard.... hope this helps...

The box office will know

I would go to the Box office and asked people which seats are which they can deftly show you on a map

Usually going to the website and verifying helps better than going and checking manually