At the beginning of Mass Effect 2, one of the optional assignments you can undertake is to visit the crash site of the Normandy to place a monument for those who didn't make it. You can also search for and uncover 20 dog tags of fallen crewmates to send to their families.
You'll earn a small bit of XP for every dog tag that you find, and you can also find some interesting data pad entries, some resources, and Shepard's old N7 helmet. There's no map in this area, but you start a little south of the NS10 shuttle when you first arrive. Here's a guide on where to find everything based on your starting position.
Dog Tag #1
As soon as you land, look to your right and you will find your first dog tag.
Dog Tag #2
Continue along the wall on your right from the last dog tag and you'll find the next inside of the remains of the cockpit.
Dog Tag #3
When you leave the cockpit, you'll see your next dog tag right in front of you (behind the rock near the shuttle).
Dog Tag #4
Turn around, and move your camera to the left of the cockpit. You should see the next dog tag in front of you.
Dog Tag #5
To the left of the last dog tag is a large yellow Fragile Crate, destroy this to find your next dog tag. There's also a Refined Element Zero just to the right of the crate.
Dog Tag #6
Turn around and head towards where a previous dog tag was in the dead-end on the immediate left, take the next left and go up the slope just above where the other dog tag was and travel to the end of the path to find another Fragile Crate with a dog tag inside.
Dog Tag #7
Dropdown just to the left of the last dog tag, there is a Refined Element Zero on your immediate left, then face forward again towards the SOS capsule and you'll find your next dog tag just to the right of it.
Dog Tag #8
Take a right from the SOS capsule and follow the path to the very end to get your next dog tag.
Dog Tag #9
Take a right and head towards the Galaxy Map wreckage. You'll see the dog tag you need in front of the wreckage, then to the right of the wreckage is XO Pressly's Datapad.
N7 Helmet
Move back in front of the wreckage and continue the path on your left (to the right of where the dog tag was). At the end of the path, you'll find Shepard's N7 Helmet.
Dog Tag #10
Head back to the front of the wreckage and face outwards. You will see the Mako in front of you stuck in a mound of snow. Head towards it and you will find the next dog tag to the right of the Mako.
Dog Tag #11
You can see the next dog tag ahead of you, just north of the last one, so run over and grab it. Then turn around and grab the Refined Element Zero on your left.
Dog Tag #12
Turn around from the Refined Element, facing into the center of the area, and you should see a Fragile Crate on the raised area in front of you. You'll need to go to the left of this raised area to get onto the slope to get to the crate. Destroy the crate to get the dog tag from inside.
Dog Tag #13
Drop down from where the crate was and follow the path in the distance that was behind the crate. At the very end of this path is a dog tag.
Dog Tag #14
Turn around and head back down the path and you'll be faced with the wreckage of the Sleeper Pod area in front of you. Head inside the wreckage to find your next dog tag.
Dog Tag #15
Go outside of the Sleeper Pod wreckage and follow it around to the left to find the next dog tag behind a rock.
Dog Tag #16
Head up the slope to the right of the last dog tag and head right. To the right of the Crew Deck wreckage is your next dog tag.
Dog Tag #17
Head inside the Crew Deck Wreckage to get your next dog tag.
Dog Tag #18
Leave the Crew Deck wreckage and in front of you is a Fragile Crate, destroy the crate to get the dog tag. Then move forwards to find a Refined Element Zero next to a chunk of ice and wreckage.
Dog Tag #19
Head left from the Refined Element Zero and you should see the next dog tag next to some wreckage.
Dog Tag #20
Turn around from the last dog tag, and go to the left of the rock that is in front of you. You should be heading towards the Normandy ship wreckage and should see the last dog just to the left of the wreckage.
