They will upvote if they have enough voting power

or steempower which enables their upvotes to be worth something or they could upvote the posts if

they think that the question is very interesting or

amazing,but i feel it is a good gesture if we all start upvoting a question or answer that we find it

interesting or learnt from it,when we do that it will

make the person who wrote the question or the answer to be encouraged to do better next time

and keep giving lovely answers by sharing their knowledge on this platform