The best place to find food street vendor

Where is the best place to find food street vendor in one place in Osaka?

Are you looking for a food street place as follows?

https://en.wikipedia.org/wiki/Regional_street_food

Then, no, Japan has no such places in general. You can see there is no "Japan" heading in the Wikipedia page.

Instead, Japan has many unique "Shopping street" and Osaka has the largest one, Tenjinbashi-suji shotengai (shopping street) or Tenjinbashi Mall.

https://www.google.com/maps/place/Tenjinbashi+mall/@34.7011524,135.511...

If you "go through" the street map view, you will see many street food venders scattered on the street. Basically, these are for take away and eating at home, but eating on the street is not prohibited. There are many cheap restaurants, and I would rather recommend you to enter into one of them. You can share your food/plate/set menus, but each of you must order at least one item.

Personally, I would check the street for street food!