What is the highest level of protection required for non-U.S. information indicated by portion markings?(TS), (//DEU C), (//GBR U), (S), (//DEU S), (//GBR C) and (C)

The highest level of protection required for non-U.S. information indicated by the portion markings is Top Secret. In this context, Top Secret is the most sensitive classification level, denoting information that, if disclosed, could cause exceptionally grave damage to national security. The portion markings you referenced provide specific classification levels associated with information from different countries, but in the realm of U.S. classification, they must align with established definitions.

The markings such as (//DEU C) and (//GBR U) refer to specific foreign countries (Germany and the United Kingdom, respectively) and their respective classification levels. While some markings denote sensitive information, none exceed the critical threshold of Top Secret that indicates an exceptionally high degree of risk. The "Secret" classification, although significant, does not provide the same stringent level of protection as Top Secret, meaning the answer leans heavily on the understanding that Top Secret represents the pinnacle of information security concerning national defense and international relations. Thus, the top level of protection indicated by those markings is indeed Top Secret.