Please find details on your first question. T140 Slot 2 is x16 width but having only x8 link to the CPU. Hence the cards in slot can only work in x8 
Hello,Q1: I want to install NVidia GTX 1080ti for computing which needs pci-e x16 in PE T140. The spec says there is a "1x8 pci-e (x16 connector)" or in another spec says "x8 link in x16 slot". I am not sure how to interpret this. Is this a pci-e x8 or x16 finally? Q2: I talked with Dell technician. He says that Dell does not support gpu cards on this server.But my question is about the possibility. Is it possible to install NVidia GTX 1080ti? Has anybody tried that?
PE T140 GPU Card Support