"Do you take a walk often?"
Translation:Ты часто гуляешь?
'Do you take a walk often' sounds bizarre and improper. Should be 'do you often take walks' or 'do you go on walks often'. The former is like asking 'do you eat that apple often'; It does not make sense because it combines a singular noun (a walk) with a repeated action. You cannot eat that specific apple often. You can only eat it once.
"Take a walk" is a common idiomatic verbal phrase. You make a good point that frequently doing the same thing could use the plural and your example with apples is correct, but to take a walk can stand alone in the singular even if the action is repetitive. It is interesting that you mentioned "go on walks" which to me sounds odd as I would more likely say, "go for a walk." English can be so frustratingly flexible.