Wo ist die Semperoper? – Die Semperoper ist in Dresden.

When someone asks for the name of a town using the question Wo …?  the answer is given with the preposition of place in + the name of the town.

Wohin möchte Chi fahren? – Chi möchte nach Dresden fahren.

When someone asks for the name of a town using the question Wohin …? the answer is given with the location preposition nach + the name of the town.