“Mao suit”.

It’s a trademark for him and his grandfather. Here he is wearing it to meet Trump:

https://www.hollywoodreporter.com/lifestyle/style/kim-jong-uns-mao-suit-was-business-as-usual-summit-was-historic-1119420/

https://en.wikipedia.org/wiki/Mao_suit

The modern Chinese tunic suit is a style of male attire originally known in China as the Zhongshan suit (simplified Chinese: 中山装; traditional Chinese: 中山裝; pinyin: Zhōngshān zhuāng) after the republican leader Sun Yat-sen (Sun Zhongshan). Sun Yat-sen introduced the style shortly after the founding of the Republic of China (1912–1949) as a form of national dress with distinct political overtones. The four pockets are said to represent the Four Virtues of propriety, justice, honesty, and shame; and the five buttons the branches of China’s former government (Executive, Legislative, Judicial, Examination, Control),[1][2][3][4][5] which still survive today in the Republic of China government of Taiwan.

After the Communist victory in the Chinese Civil War and the establishment of the People’s Republic of China in 1949, such suits came to be worn widely by male citizens and government leaders as a symbol of proletarian unity and an Eastern counterpart to the Western business suit. The name “Mao suit” comes from Chinese Communist Mao Zedong’s fondness for the style. The garment became closely associated with him and with Chinese Communism. Mao’s cut of the suit was influenced by the Stalin tunic then prevalent among Soviet officials.[6] Although it declined in use among the general public in the 1980s and 1990s due to the increasing prominence of the business suit, it is still commonly worn by Chinese leaders during important state ceremonies and functions.[7][8] The Mao suit was also worn in North Korea by party elites.

In the 1960s and 1970s, the Mao suit became fashionable among Western European, Australian, and New Zealander socialists and intellectuals.[9] It was sometimes worn over a turtleneck.

The Mao suit is worn at the most formal ceremonies as a symbol of national sovereignty. China’s paramount leaders always wear Mao suits for military parades in Beijing, even though other Politburo Standing Committee members and other Politburo officials wear European business suits. It is customary for Chinese leaders to wear Mao suits when attending state dinners.[13][14][15] In this situation, the Mao suit serves as a form of evening dress, equivalent to a military uniform for a monarch, or a tuxedo for a paramount leader.

The Mao suit also serves as a diplomatic uniform. Although Chinese ambassadors usually wear European business suits, many Chinese ambassadors choose to wear a Mao suit when they present their credentials to the head of state.[16][17][18] The presentation ceremony is symbolic of the diplomatic recognition that exists between the two countries, so it carries a higher level of formality than other diplomatic meetings.