There are 15 in-game trophies to collect, 9 of them are found scattered throughout the planets and 6 are awarded as part of obtaining all Titanium Bolts and Skill Points, all Health and Weapon Upgrades, and completing all Annihilation Nation and Ranger Missions. To obtain the  Hero of the Galaxy platinum, you only need to collect the Ratchet and Clank collectible trophies, and acquire all of the completion trophies.  But for those you of who search far and wide, there is a special award if you find all 15 in-game trophies!

The Clank trophy is obtained at the Holostar Studios, while playing as Ratchet.
 

Upon this ledge to the left of the elevator awaits the Clank trophy.

After exiting a cemetery themed set, you will come across a street with several enemies to dispatch. An elevator that needs you to solve a Hacker puzzle to activate it will be nearby a Gadgetron vendor. Once the elevator is activated, ride the elevator to the top.
At the top, immediately double-jump to a high ledge on the left instead of continuing forward, and on this ledge the Clank trophy awaits you.