Ask this in the simple questions topic the next time you have questions like this! It's a random world BOE.
Look up any drop you want in WoWhead, if it's a random world drop, you'll see that it drops from several monsters with a low drop percentages, these drops weren't meant to be farmed, they were ment to be sold in the auction house by low level toons as an early source of income, as the drops are completely random and aren't suited to your class specifically (but can be by chance)
When you look for how to farm these items, in the WoWhead drop table, look for the lowest level monster that drops it, and the highest level monster that drops it.
In the case of Prospector's cloak, Any level 12-18 monster can drop it.
Hope this helps.