A PIP doesn't have targets the employee doesn't know about - not formally, anyways. The targets are the same whether you're on a PIP or not: meeting expectations for your level. At a company like Amazon these are going to be well defined and published. The manager would have also more than likely, if acting in good faith, found you a mentor by this point. If they weren't acting in good faith, then it doesn't matter whether you know about your PIP or not, meet your expectations or not, you're cooked.

But yes, I agree, you should pull the ripcord as soon as you get a good sense of what's going on.