That's quite an accomplishment. I hear that people who get a reward check from him for errata or other help usually frame them instead of cashing them.
FYI, he stopped sending checks back in 2008 due to check fraud: https://en.wikipedia.org/wiki/Knuth_reward_check. It's a shame. I had a professor that had received one for finding a bug somewhere and he proudly displayed it in his office. It was a pretty good conversation starter.
And, at least in my case, he included a comic strip of a guy cashing a cheque at the bank, being asked by the bank teller what he got this cheque for. "Three dollars? You sure work cheap!".
Lockheed's legendary Kelly Johnson was said to have given quarters to anyone at the Skunkworks who won a technical bet off of him. I believe these were also treasured by those who got them.
According to this, he has a secretary that filters messages for him: https://www-cs-faculty.stanford.edu/~knuth/email.html