any bus or train from dunhuang to turpan in xinjiang? how to buy the tickets?

First, you need to take a bus from DH bus station to Liuyuan.
Then, walk northeast for 3 minutes to Liuyuan Railway station. Take a normal train to Turpan; or take a taxi to Liuyuan South Railway station and take a bullet train to Turpan.

The normal train takes about 6-7h and CNY93; the bullet one takes about 3h 40 minutes and CNY195.5 for a second class seat, CNY234.5 for a first one.

All the tickets can be bought at the ticket counter in the bus/railway station.