How would one say "I do not know whom he visited yesterday"?
You just have to switch some cases around "O dün kimi ziyaret etmiş, bilmiyorum." There are other ways to word this as well.
Does the main verb (bilmiyorum) have to go after the indirect discourse?
It normally goes at the end :)
My translation should have been accepted: I don't know who paid him a visit yesterday. "To pay someone a visit" and "to visit someone" are equivalent.
I am not a native English speaker, but I would understand your sentence as if anybody paid (money) for the visit.
No,it is a common way to say to visit someone - to pay someone a visit
Believe me I feel many times that I have to remould my English to be suitable for your translations which are so strict.
Why "has visited" is wrong?
"has visited" is the present perfect tense and is used for ongoing action that has happened in the past (and in a few other cases). In this case, the action is completed and there is no time expression. :) It has to be simple past tense.
Oops, sorry, I wanted to ask "had visited", and tanx for your quick response
That would be "etmişti" in that case :)