Either from Shanghai or Beijing, you could take train to Urumqi first and then to Kashgar. If you’d like to visit the scenic spots around, you would better join a tour group there, which will be safe and economical for you. For detailed attractions in Urumqi and Kashgar, you could refer to the pages:
https://www.travelchinaguide.com/cityguides/kashgar.htm
https://www.travelchinaguide.com/cityguides/urumqi.htm