Dojo as a translation comes from the fact that the same term was borrowed with Japanese pronunciation. The missing “ng” is a feature of old Japanese borrowings from Chinese; at the time the “ng” nasalized and lengthened the preceding vowel which shows up as long vowels today.
〈도장〉 (dojang)/〈どうじょう〉 (dōjō)
〈영〉 (yeong)/〈れい〉 (rē)
〈생〉 (saeng)/〈せい〉 (sē)
〈능력〉 (neungryeok)/〈のうりょく〉 (nōryoku)