They don't have the thoughts that you list because talking doesn't cause them anxiety and they don't have any issue producing speech, they are not fixated on speech. It's like asking what we think about our heart beat, you only think about it when you're already anxious and it is racing. Being fixated on speech only worsens stammering imho, focusing on what your goal is / what you want to communicate and not allowing stammers or blocks to deter you instead is the thing that helps me.