The attachment points depend entirely on the model.
As a general rule, though, most models have origin and overhead, and most unit models have head, chest, "hand,left", and "hand,right". Most special effects models, though, have none. A lot of mounted models have "chest,left" and "chest,right", and some models have "foot,left" and "foot,right". To really know, you'd almost have to open the model file up for yourself to see.