It did took me a long time to figure this one out, i didn't got it on my
first play-trough. But with a little logical thinking ;-) i got it: i quote the
achievement: "A true metro citizen. You know everyone and have
seen everything." So i started from the level hunter again, and i finally
found what to do to get this Achievement: Just start from the level
'Hunter' and talk to everyone, knock on every door (multiple times)
and listen to what the people have to say. even listen to conversations
between other persons. sometimes you'll get a white 'flashback' like
flash (i think these are the ones you'll need). Talk to the doctor, the
people waiting at the entrance etc. search every store and look at
everyone a couple of seconds and wait until they start talking and
let them finish (or keep pressing X together with looking at them).
Repeat this process in the next level (Chapter 2 - Exhibition).
My advice is to continue playing from Hunter to Exhibition my
experience in quiting and selecting the next level is that it results
in not getting the Achievement. Also take extra care in listening to
all the conversations here, Give the man the money/cartridges
for the medicine (the man on the bench next to the teddy and
women). in the diner/bar there are two man negotiating about a deal
listen to them first then get close he tells you to get lost, stay
anyway and listen to their short conversation; you'll get another
'flashback' moment here.
After passing the guitar playing resident enter the half closed room,
here you will encounter your stepfather, talk to him by pressing X
and let him finish, repeat this a couple of times until you can't start
another conversation, then get to the train-cart en talk to the
"captain-like-guy" let him finish and tell him that you are NOT READY.
He will tell you something like "Get your gear, you'll have a minute".
After this, return to your stepfather and talk to him again. This was the
'flashback' moment where i got my achievement.
Also keep in mind that i helped-out all the homeless/hobbo's i
encountered on my journey (also in my first play-trough).
I really hope this guide helps some people out, because for me
it was a pain in the ass this achievement.
Have fun hunting and good luck.