The title says all. This I have been wondering for some time. I assume the answer is no; else I suppose I would have noticed him.
(I hope I do not break any rules by asking this.)
don's personal presence on the internet is essentially limited to his web pages at stanford.
on his tex page he lists a contact for reporting "purported errors". this still happens to be me, although the duty was officially turned over to karl berry as of 1 january 2015.
as don has said many times, he does not have an e-mail address; he relies on the good offices of a secretary to communicate urgent messages. his next scheduled tex review is in 2020, and he won't even look at tex and friends (except as a user, for his own work) until then.
The only way to gain enough efficiency to complete The Art of Computer Programming is to operate in batch mode, concentrating intensively and uninterruptedly on one subject at a time, rather than swapping a number of topics in and out of my head.
This unambiguously means that unless he’s working on a TeX chapter right now (which I’m assuming to not be the case just by a stochastic estimate) he will be buried very deeply into a subject that is not TeX and therefore see no time to answer any TeX questions as interesting as they may seem.