There is no cheat code to unlock Cosmic Spider-Man in Spider-Man: Shattered Dimensions on Xbox 360 (or any platform).
Cosmic Spider-Man is a pre-order bonus / DLC skin (GameStop exclusive in US). It was a downloadable code redeemed on Xbox Live Marketplace (now delisted). The skin is not on-disc unlockable.
The game has no cheat code menu; cheats do not exist for this title. All suits are unlocked via story progression or were DLC.
On PC, mods can add the skin; on 360, it is unobtainable now unless you have an unused original code (extremely rare).