Gmail keyboard shortcut to jump to specific label

AFAIK, you cannot choose a shortcut for a custom label.

Anyway, you can access gmail default label with shortcuts :

^b chats
^f sent mail
^i inbox
^k trash
^r draft
^s spam
^t starred messages
^u unread mail

Or, you can use l to access the label menu (described here) and then choose your label.

And btw, here is a cheatsheet for Gmail shortcut.