Is a contra account a debit or a credit?

That depends, it could be either. a contra-asset account would be just the opposite of an asset. All assets have a debit balance (increase with debit) therefore a contra-asset account would be a credit.

The same holds true with a contra-liability account, it is just the opposite, a liability maintains a credit balance (increases with a credit) therefore a contra-liability account would be a debit.