How to fix the variable names in a simplenews subscription confirmation mail?
I am guessing you upgraded from D6. The tokens you are using are D6 tokens.

Go to /admin/config/services/simplenews/settings/subscription and change the tokens. For instance, the default subject for D7 is :

Confirmation for [simplenews-category:name] from [site:name]


Note the new (D7) token format. You can find he new tokens by expanding 'Replacement patterns'.