Translation:I do not know when he will come here.
hier = here
hierher = to here
Thus, "Ich bin hier", but "Er kommt hierher".
And when do you use just 'her'? For example one of the sentences in this lesson is 'Kommt sie her?'
I don't know when he will come this way should be accepted. This way was the translation of hierher in an earlier exercise
"I don't know when he will come this way". Not accepted yet. I also reported it.
Why was "I don't know when he is coming here" marked wrong? I am not English, but I think it means the same
You're right Sydney. In English, we often use the present tense, especially with verbs like TO COME, to imply a future action or event. In fact, it is more common to hear "I don't know when he's coming" than "... when he will come". The context makes it obvious that what you're talking about hasn't happened yet. Have noticed that this is also fairly common in German.