"Yunanistan'dayken Türkiye'yi çok özledi" seems also possible
It has been added. It had been glossed over since it is the -miş skill :)
Can we include O to emphasis that it is he that is doing the missing?
That would be correct too. Though it's fine to omit since the subject is also contained in the verb "özlemiş".
Can you say Türkiye'yi çok özlemiş yunanistan'dayken ?
It's an inverted sentence
I think that the verb must be at the end of the sentence, and the place have to be at the beginning if the subject is not mentioned.
Why is it "Türkiye'yi"? I don't really understand the yi in here.
It is in the accusative case. It is the direct object of the verb "özlemek"
Is accusative case always used with özlemek?
Not necessarily, but Turkey is a specific concept (you are talking about a specific place). Because of this, it is a specific direct object here so it requires the accusative.
Ah I think I get it, thanks!
I think yes, I cannot think of an exception
How does "Yunanistan'dayken" mean "While he was in Greece"? Could anyone break it up (suffix by suffix) for me please?
literally "Greece-in-While". It could be any subject but we know from the main verb that it was he/she/it. If it were another person, it would be indicated, for example "Ben Yunanistan'dayken, Alex Türkiye'yi özlemiş"
İ see now. Thanks a lot