Anyway to obtain longclaw without murdering jon snow?

[Gannorton]

Because obviously you can send him to the wall to get it.

[H3YimDR3W]

In short, no. Other than using the cheat menu which means editing your menus.txt file and using the in-game console. (This may cause errors)

[Skyler Blackfyre]

But how to kill Jon Snow? I could not capture him after battle.

[H3YimDR3W]

You can't kill him or get longclaw.