If you would like to spend for training you can go with Udemy videos from Zeal Vora and Bryan Krause, both has covered over all technical part of Vault, also they are providing some valuable hints to clear the exam.
Should go through HashiCorp Vault official documents and try to match the topics with day to day use cases and BAU scenarios, that will help in the exam.
Most of the operational questions will come based on scenario.
Get some strong knowledge and understand the concept of vault Architecture, Tokens and Policies.
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