Tome of Fleeting Knowledge
Wondrous item, Legendary (requires attunement by a wizard or warlock)
Once per long rest, you can consult this tome to gain double your proficiency bonus on an Intelligence skill check, learn to read or speak a language, or a similar feature for the next hour. Certain incomprehensible languages or powerful features may result in a level of Exhaustion.
This is very similar to Agon’s divine item from the Haven campaign. It has been very useful to the campaign. One of the things that has hit him hard is using the tome to read fey.