"I am at work."
Translation:Jestem w pracy.
No, it's locative. The fact that English uses 'at' here and not simple 'in' is irrelevant. Locative officially answers the questions "about whom?, about what?", but also the more 'logical' (given its name) "in whom? (sexual alert! but seriously, e.g. "to be in love 'in' someone" - być W kimś zakochanym), in what?".
This here is "I am in what?" - Jestem w pracy.