Dan Luke wrote:
An aircraft departing a class D airport next to class C airspace
requests VFR flight following and is assigned a squawk code. The
aircraft is cleared for takeoff and instructed to fly runway heading at
or below 1,700.

Why? It's a class D airport. This should have been immediately questioned.


A few moments after takeoff, the pilot is instructed to
contact Approach but is unsuccessful after several attempts. The
aircraft nears clouds that extend well above and below its altitude and
will break VFR if it continues on its present heading. Still unable to
contact Approach, the pilot turns to maintain VFR and passes close to an
airliner inbound to the Class C airport, causing a loss of separation
incident. Who will suffer a violation, the pilot, the TRACON
controller, or both?

There is no standard separation between those two. If they missed then
there was no loss of separation. If it happened inside of class C then
the VFR pilot can get dinged for not establishing comm before entering
the class C. The TRACON controller is not a factor.