"Can you tell me why you are doing that?"
Translation:Ĉu vi povas diri al mi, kial vi faras tion?
Because "me" here is the indirect object of the sentence (tell something to someone), which is different than, let's say, helping someone (help me, not "help to me"; " me is the direct object here).
I remember the fact that diri takes an indirect object by thinking of it as closer to english "say" than "tell"
You wouldn't say "Can you say me why you are doing that?" but rather "Can you say to me why you are doing that?"
So "povas" can be used in this way? I thought it meant strictly only "can" (whether you are able to do something), and that our usage of "can" in English is unique? After all this sentence is not asking "Are you able to tell me why you are doing that" is it? Wouldn't it be better translated with something along the lines of "please"?
Mi havas samegegajn pension. Esperanto shouldn't borrow idiomatic expressions from markings as much as possible. As an English speaker this sentence is perfectly understandable, but it might not be so for speakers of other languages who don't use such an expression.
The only possible reason I could think of is that many languages use such a construction, but I doubt that is the case.
If you are referring to the model answer or similar variants, it's because povas is the main verb (or whatever the proper grammar term should be), diri is being used as a sort of noun here, an action acted upon by povas.