Can I pursue PG in dermatology after completing B.Tech?

You won't be allowed for PG in dermatology without completing your MBBS degree. It's a post graduation course for medical students & not for engineering students.

In order to pursue MD Dermatology or Diploma in Dermatology the eligibility criteria is degree, such as MBBS. Therefore, based on your engineering degree, you are not eligible for PG or Diploma course in Dermatology.