From Pindi, u can go to Murree or Abbotabad using Daewoo bus or other coaster/ hiace. From there, u will get public transport (mainly carry daba charging per passenger) for Nathiagali/ Dungagali. Mushkpuri trek can be done from both place i.e. either Nathiagali or Dungagali.
The best is to start from Nathiagali side and descent towards Dungagali side.