Breakdown of Wo kommt dieser Mann her?
der Mann
the man
kommen
to come
wo
where
dieser
this / that (fem.: diese, neut.: dieses)
Questions & Answers about Wo kommt dieser Mann her?
I learned that "where from" is woher. Why are wo and her split up here?
In spoken German, it is very common to split words like woher (where from) and wohin (where to). The wo stays at the beginning as the question word, and the directional adverb her is pushed to the very end of the sentence. Both Woher kommt dieser Mann? and Wo kommt dieser Mann her? are completely correct and mean exactly the same thing.
Why do we use her instead of hin in this sentence?
The word her describes movement towards the speaker, while hin describes movement away from the speaker. Because the man is coming from somewhere else to where the speaker is right now, we use her. If you were asking where the man is going (moving away from you), you would use hin: Wo geht dieser Mann hin? (Where is this man going to?).
Why is it dieser Mann with an -er ending instead of diesen Mann?
dieser Mann is the subject of the sentence—he is the person doing the action of coming. Because of this, it has to be in the nominative case, which takes the -er ending for masculine nouns. You would only use diesen if the man was the direct object receiving an action, like in the accusative sentence Ich kenne diesen Mann (I know this man).