An .obj file written by OSM2World will always contain the latitude and longitude of the origin as a plaintext comment. The comment looks somewhat like this:
# This file was created by OSM2World 0.2.0 - http://osm2world.org
# Projection information:
# Coordinate origin (0,0,0): lat 48.573213949999996, lon 13.464217200000022, ele 0
# North direction: (0.0, 0.0, -1.0)
# 1 coordinate unit corresponds to roughly 1 m in reality
I believe there’s no standard way to add such information to an .obj file, unfortunately, which is why I used a comment. But maybe that is something you can work with?