Which one is the correct A. Look at that school where I used to go there
B. Look at that school which I used to go there

It's A. Also notice that both of those sentences should not have 'there' in them or both of them will be deemed incorrect.

cassius, casca, and their allies plant false documents to manipulate brutus to join their cause to remove caesar. after doing so, they visit brutus at night in his home to persuade him of their views. there they plan caesar's death. brutus is troubled but refuses to confide in his devoted wife, portia. on 15 march, caesar's wife, calpurnia, urges him not to go to the senate. she has had visionary dreams and fears the portents of the overnight storms.

a. is the correct answer