If the obj is part of a figure or prop then it will be either in runtime/geometries/vendor/product where vendor is the vendor name and product is the product name.  Sometines vendors put the obj in the same folder as the figure or prop. ContentParadise is know for that. 

Poser tends to embed the geometry file in a prop if you import an obj and then save it as a prop. You can extract the obj from the prop with Geomstripper (freesruff) but its not required.