"적이" also translates as "ever". Thus, the question ican be transpated into english as "Have you ever worked in Korea?"
(은/ㄴ) 적이 있다/없다 is a form you can add on to the end that adds the meaning "to have ever or have never done something." Usually you would see 아/어 본 적이 있다/없다. Which is "have you ever/never tried to do something."
적이 does not mean has p.p.
p.p = past participle
what does it mean?
I've realised that it means past participle used to form the present perfect
Like: I have done, you have been, he has worked, we have seen
Have you ever worked in Korea might be more accurate? You're doing a great job, Duolingo team :*