"Genned up" is a British phrase used to describe someone who is well-informed or knowledgeable about a particular topic. Other synonyms for "genned up" include "clued up," "in the know," "well-versed," "well-read," "familiar," and "versed." These words convey a similar sentiment of someone who has a good understanding of a topic or situation. Other phrases that can be used in place of "genned up" include "up-to-date," "educated," "skilled," and "proficient." Having a broad vocabulary of synonyms can help you more effectively convey different shades of meaning and nuances in your writing or conversation.