Orbitals

How two electrons occupying an orbital are distinguished?

When two electrons are present in the same orbital, they should have opposite spins. So spin quantum number distinguishes between two electrons.

Where will enter the electron when 6d orbital is complete?

The sub shells are arranged according to (n+l) rule and according to Aufbau principle, the electrons should be filled in energy sub-shells in the order of increasing energy values. When 6d orbital is complete, the entering electron will go into 7p.