There may be some plumbing jobs available in Phoenix for licensed contractors. Just look in the newspaper classifieds or call up some local plumbing businesses to see if they are hiring.
This question is difficult to answerl because it is so vague. If you would consider narrowing down your question to a country, state, industry etc., it may be possible to give you a better answer....
I'm not sure if you are trying to say - how many jobs are there IN THE WORLD - but it is hard to tell because there are so many different versions of a job. one job may have many other jobs working...
Either a 4 year Degree in engineering plus 4 years in the profession for a masters license (Depending on which country /state your inOr 10,000 hour apprenticeship and 744 hours of class room studies...