The winding mountain roads make travel slow and dangerous. I looked at a map and figured a couple of hours from Kukes to Rreshen, but in fact it took almost 6 hours of slow going.
Albanian public transport is very third-world. At each town taxi park there is a motley assortment of minibuses and drivers. The vehicles are often not marked as to their destination, so you have to ask around. There is no fixed schedule -- you wait until the bus or taxi has filled up.
The minibus park is at the entrance to the town, but there are a couple of scheduled buses that stop at the town's main intersection (not up the hill). The town is so small that you will have no trouble finding either site, but just be sure you know that there are two different bus stops.