Which is correct:了 or 过 in 我去。。。他家，知道他住在哪里
了 indicates the verb is 'completed action'
过 indicates the verb is 'experienced action'
我去过 他家，知道他住在哪里.  (I had gone to his house before,  so I know where he lives) is the correct one
去过 = had gone before
去了 = have gone to