how can I get from Turfan to Dunhuang

There is no direct train from Turpan to Dunhuang. You may take train from Turpan to Liuyuan. Then walk about 100 meters toward south to find Liuyuan Bus Station. There you can catch bus to Dunhuang. It costs around CNY 20. There also many taxis or vans outside of the railway station. You can rent a taxi together with others. Usually, a taxi accommodates four passengers. It costs CNY 30 to 50 per person.