I know that the city sewer line is behind my home and the water line is in front of my home. My home was built in the 50's. Do I have a clean out? I even know where the pipes come from my bathroom to the ground (single story home with crawl space). How will I know where to dig and how deep to go?

I think the easiest and in my experience it's been a free service if you call the city/county/town that is responsible for your sewer and water service. They will likely send someone out to locate, mark and flag your sewer and water lines. Obviously when you call the city they'll let you know if there is a charge or if it's free. This service is usually universal for things like gas lines and electrical lines (if they're in the ground) and it shouldn't matter if you're planning on digging up the ground to build or landscape or you just simply want to access the sewer. To me this would be the easiest way to answer your question. Otherwise it might be like a needle in a hay stack to track where all your underground utilities are.

First many homes built in those years did not have one, so you may not have one, Have you looked where the pipes come into the crawl space, some silly contractors actually put them in the crawl space back then also. Next of course as noted, a service can run a camera though the line and see if there is one and where it is.

Also of course some use the vent pipe on the roof as a clean out.