In several non-computer-sciences SEs I came across users which have gathered a lot of reputation because they give excellent answers.
I observed that some of them never have upvoted questions even though have answered 1000s.
Personally I upvote questions when I consider the question useful or simply when it is good style, on-topic and/or well written.
How can I encourage a user to upvote a question? How can I politely and context-correctly make sure that this user is aware that questions can be upvoted and that this is actually useful? And if in doubt, how can I initiate a discussion about it with this user?