If you meant where you get that dagger, you can only get it as a city elf, if you were good in the beginning, you get it after you finish the alienage in denerim, your father gives it to you, but since your only level 12 i assume you aren't there yet sadly :(
Best dagger in the game is rose's thorn, hands down. It can be bought in orzimmar.
These are also other solutions: Dead Gods: There are 3 of these, each of different tier, one can be bought in lothering, one can be stolen from lord dace (orzimmar, bhelen side), last and best of the 3 can be found in the deep roads i believe. Stone prisoner DLC brings two good daggers, one of them endgame-worthy; one where you find shale, and one during shale's quest. The Edge is a dlc weapon that is not bad at all. There's also a dead thaig dagger or something on the deep roads.
I think some one mentioned it earlier its by reading the various codex entries through caridin's cross (or was it ortain thaig?) and when you read the last required one you will get a quest, the reward can be found with the map marker, its in a corner some where i know that much