If a individual was forced to live in a urban enviroment off the grid,for whatever reson,ie living on the streets.

One can still continue their life.

How does one go about learning living on the streets skills, if one has never been there?

Every city has homeless shelter/homeless camps/homeless individuals.

Go to one of these places strike up a conversation with different individuals.Find out who is the most knowlegdable on how to survive on the streets.

It might cost you a pack of smokes or a few bucks or even a cheese burger or 2.

Once you gain your intell on individual/individuals explain to them what and why to a point, of why you want to know street skills.
IE safest/places to sleep-food banks food shelters-best places to dumpster dive at etc.

Another thing to do is find and recon all parks/swamps/vacant woode lots etc. for yourself.

Not all homeless know about all things.

It is better to know about something beforehand. If it might be in one near future.

Preparation is the key to surviving a bad situation.