the "to postposition is unnecessary here, as the interrogative "where"already implies a direction. We say "Where are you going", rather than "where to are you going without me. But then, I believe that the "to", if included, should come straight after the "where"word.
You do have the "Where to?"question frequently used. - "I shall be moving soon." -"Where to?" I think that what feels wrong is mainly the positioning of the "to"in the correction.
To those who think it’s a valid rule that a sentence should not end with a preposition, I challenge you to fix this sentence: This dress is not paid for. And don’t try to wiggle out by saying “money was not paid for this dress.” What, are we in a place with the barter system?
Yes, both are where, but איפה (and also כאן) means where, when you are asking about the location: איפה אתה עובד? "Where are you working?" On the other hand לאן means where or where to - and you use it to ask about the direction of somebody's movement: לאן אתה הולך? "Where are you going?"