"Where are you, usually?"
Translation:Hvor plejer I at være?
As a German speaker, it helps me a lot to translate plejer (at gøre noget) in my head with the rather archaic pflegen (etwas zu tun).
I managed to get the "Hvor plejer du" but why is there "at vaere"? is "at vaere" not to be and if that is correct, why is it in this sentence?
Well there's a conjugated form of to be in the English version as well (are). In the Danish construction, there are two verbs: at pleje and at være.
The first verb, pleje is conjugated in the present => plejer
This second verb, therefore, is left as an infinitive => at være
I think your problem here is that there isn't an English equivalent of at pleje, since the adverb usually is used for that meaning.