Why is reykjavik most northern capital when nuuk is further north?

Answer 1

Both are true. Reykjavik is the most northerly capital of a sovereign state, but Greenland is an autonomous dependent territory of Denmark, so by that measure Nuuk doesn't qualify.

Answer 2

Reykjavik is considered the world's most northern capital because it is located at a higher latitude in comparison to Nuuk, the capital of Greenland. While Nuuk is further north in terms of general geographic location, Reykjavik is officially recognized as the northernmost capital city based on political and administrative criteria.