Kosovo doesn't have an ISO country code because its declaration of independence from Serbia is still not universally recognized. In particular, Russia does not recognize Kosovo, and has opposed giving Kosovo any of the trappings of an independent nation unless an agreement can be reached between the governments of Kosovo and Serbia.
Yes, Slovenia's ISO 3166-1 country code is SI.
Slovenia's telephone country code is +386.
Slovenia is country code +386.
The country code and area code of Celje, Slovenia is 386, (0)3.
The country code and area code of Kranj, Slovenia is 386, (0)4.
The country code and area code of Krsko, Slovenia is 386, (0)7.
The country code and area code of Maribor, Slovenia is 386, (0)2.
Per Wikipedia, the ISO country code "KP" is North Korea. Seoul is in South Korea, whose ISO country code is "KR".
The country code and area code of Kotor, Montenegro is 382, (0)82.
DK is the ISO-3166-1 country code for Denmark.
FM is the ISO country code for the Federated States of Micronesia in the Pacific.
Yes, country code top-level domains are assigned based on ISO-3166 country codes, which are protected globally. (Except that the United Kingdom uses .uk instead of its ISO-3166 code of .gb; however, the ISO has agreed not to assign UK as an ISO-3166 code.)
The ISO-3166-1 country code "SE" is Sweden.
SVK is the ISO country code for Slovakia.