Nowhere, but you have to do it anyways. The only hard rule is to not do it while they are working.

>>34398841
>In which social environments
Social environments.
>gym, supermarket, retail store
None of these, they aren't social environments, they're public spaces. People are there to perform an action and leave. It's absolutely going to result in a negative response cold approaching people here, and if you make them uncomfortable they're forced to choose between leaving early and finishing the task they're there for.
>park
Acceptable because it's a social environment. Albeit most people there are likely there to socialize with people they know. A better environment would be a club or bar. But cold approaching has a poor success rate, and most social environments are not places where cold approaching is even realistically possible because they're recurring places. Things like clubs, classes, or other areas that let you get to know someone casually enough that you can decide to invite them somewhere else. This will have a better success rate than cold approaching as well, particularly if you learn to recognize signs of interest and express your own before asking someone on a date.
>>34398847
You definitely do not have to cold approach. It's the absolute worst way to find a partner, even compared to dating apps, and that's saying something.