If you have 2 "layers" of geometry in the model then it might be poke-thru you're seeing in those black lines. That's what it looks like to me. Could also be a combination of that and whatever bump you have set on the material. 

Clothing should only be one layer, all normals facing out (away from the figure). The geometry is actually paper thin so to acheive the illusion of actual cloth and thickness, you use the proper combination of material settings, bump, normal and displacement maps. 

 

~Shane