Pure phonetic rendering: 唐恩 'Tang-en' = 'Dunkin' (the n is split across syllables Mandarin-style), 都乐 'Dou-le' = 'Donuts'. The choice of characters is mildly auspicious - 唐 (Tang dynasty), 恩 (kindness), 都 (capital), 乐 (joy) - but no semantic content.
culture
The brand globally rebranded from 'Dunkin' Donuts' to just 'Dunkin'' in 2018, but the Chinese name kept 都乐 'donuts' baked in. Less ubiquitous in China than Starbucks (星巴克) or Luckin (瑞幸), with a presence concentrated in tier-one cities.
