We don't have synonyms for jo'burg yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are joburg.
(n) :
Alternative spelling of Joburg. [(chiefly South Africa, Zimbabwe, colloquial) Syllabic abbreviation of Johannesburg: the largest city in South Africa, in Gauteng province.]
(n) :
Alternative spelling of Joburg. [(chiefly South Africa, Zimbabwe, colloquial) Syllabic abbreviation of Johannesburg: the largest city in South Africa, in Gauteng province.]