where do I go to get this mission in game? Sorry I meant wasteland sewers mission

Yeah, I'd like to know, too. Although, to be honest, I haven't done much exploring of all the little 'hatches' you can see scattered about.

I have not started the game yet but I think they are sewer hatches around the wasteland.

It's right in front of where you come out of your ark in the beginning, there's a guy at a stand under an overpass - I hope that helps, I don't know how else to describe it.