Hi,
Having a job offer is definitely an added advantage, but its not essential to get successful nomination of subclass 190. It depends of range of factors such as your employability prospects in the state, ties to the NT such as family/friends, financial capability so as not to depend on state in case you don't find employment & your commitment statement of course (You can provide this evidence by contacting potential employers and provide that as an evidence of your commitment/seriousness).