A person shouldn't be given a position in high-ranking government office without having a vast understanding of what their job entails and how to handle the issues they will be dealing with. That would be like asking a bartender to be a rocket scientist, although he has no knowledge in the subject whatsoever.
Yes, officials should be asked to prove their knowledge before being given a post. Otherwise, these people will say anything in order to get the position they desire, without having the proper credentials. Then, distrust and confusing will ensue within the country regarding the topic the official is not informed on.
Yes, officials should be asked to prove their knowledge before being given a post because they are supposed to come up with the answers. If they do not know enough about the position or their country, how can they properly serve it? They must understand basic information to reach such levels.
Not every government official is going to know everything about everyone. There is no way that a politician could know about every issue that is going on both domestically and in the world. They can learn what they need to know as events develop. The most important thing is that they have sound judgment.