Just beat the game and find all of the collectibles in each level, nothing to do with any extra content added for this version. After finishing the game > Select Scene. Once you have finished an entire act, it shows 100% underneath and a 100% note clipped to the picture. Click on an unfinished act, and scroll through all the scenes, checking the stats to see if you have all the magnifying glasses, diary pages, and the handheld game (there is only one handheld game in each act). I have nothing to do with 360GameTV but they have made a fantastic collectible video here. Once you have all the collectibles in a scene, back out to the Main Menu and select the next scene you need.
Unlike the 360 version, collectibles save immediately. It doesn't show a save animation, but when you back out to the Main Menu, your collectibles are retained. I even tried dashboarding instead of Main Menu just to check, and it still saved them.
There are links to each scene if you visit the page. I will just paste their non-linked time markers, complete with German.
Act 1 - Welcome to Seattle - Willkommen in Seattle
00:12 - Left Behind - Zurückgelassen
00:48 - End of the Tunnel - Das Ende des Tunnels
01:17 - Welcome to Seattle - Willkommen in Seattle
01:55 - Outskirts - Vororte
03:04 - A Chance Meeting - Zufallstreffen
03:36 - Checkpoint Charlie
04:37 - Broken Homes - Zerstörte Häuser
05:44 - Lous Pawnshop - Lous Pfandleihe
Act 2 - Hunters - Jäger
06:15 - Tunnel Rats - Tunnelratten
07:12 - The Collector - Der Sammler
07:31 - The Den - Die Grube
08:43 - Ascend - Abstieg
09:39 - Tree House - Baumhaus
10:52 - The Big Bird - Der große Vogel
11:12 - Lydia
11:29 - Human Flow - Menschenstrom
12:20 - Playoff - Entscheidungen
13:28 - Emergencies - Notfälle
14:29 - Medicineman - Medizinmann
Act 3 - The New Law - Das neue Gesetz
15:27 - Fallen - Gefallen
16:56 - On Air - Auf Sendung
18:04 - Arcadia
19:16 - Revelation - Offenbarung