error: expected primary-expression before '.' token

DaveGray65:
Also, when you say code tags, is that the </> icon on the top of the message entry box?

Yes. See how much nicer it looks if you do it that way. Plus, others can easily copy your code (click 'select', then ctrl-c) and paste it into their IDE. Always good to make it easier for those who are trying to help you.

#include <PID_v1.h>

// This program isolates the GetKp problem

double KpSet ;  // PID GAIN currently set in the PID instruction

void setup() {
  // setup code
  KpSet = PID.GetKp();
}

void loop() {
  //
}