There are several synonyms that we can use instead of the phrase "not understand all one knows." Some of the alternatives include confusion, perplexity, bewilderment, incomprehension, and puzzlement. Whenever we encounter a complex issue or subject matter that we don't fully understand, we may feel confused or perplexed. Likewise, when we find a problem challenging to solve or a concept difficult to grasp, we may be left feeling bewildered or puzzled. Therefore, the choice of synonym will depend on the context in which it is used, as well as the level of understanding required for the matter at hand.