The Art of The Batman mentions that the pants are supposed to be US surplus, so I think they're
black M65 pants:
There's also a photo of an earlier version of Riddler's costume on set at the mayor's house. It has the question mark on the black panel like the McFarlane DC Multiverse figure and Lego Minifigure and the mouthpiece on the cold weather mask has a button like the real one does:
And there's another shot where he has no question mark and the button where it's supposed to be is still attached. I believe this is how he appeared in that scene in the movie:
BTW, did anyone else notice that the first Riddler follower who's at Gotham Square Garden also had the button on his cold weather mask's mouthpiece? You can kinda see it in this screenshot:
