You should easily obtain this trophy through normal progression of the game, despite how much 42.195km actually is, you get it quite easily. There is really only one tip to make sure you get this, which even if you don't listen, you should get it or get very close to the trophy still, this tip being;
Don't use taxi's, run everywhere, as this'll help you much much more with your km's travelled.
If you want to check on how much distance you have travelled on foot, just go back to whereever your hideout currently is in the game, I obtained this in chapter 5-6, so my hideout was the Serena bar in Tokyo. In your hideout, you get the option to save, move items, reminisce, and check your stats. Just simple go on your stats and it's there.