Use this syntax to access custom labels in Lightning components:
1.$Label.c.labelName for the default namespace
2.$Label.namespace.labelName if your org has a namespace, or to access a label in a managed package
Here are some examples.
1.Label in a markup expression using the default namespace
{!$Label.c.labelName}
2.Label in JavaScript code if your org has a namespace
$A.get(“$Label.namespace.labelName”)