"Attitude towards" is commonly used, but there are cases that "to" can be used as well. It depends on the sentence. Ex 1: She has a positive attitude towards studying. (In this case, "to" would not sound right) Ex. 2: She has always been positive to everyone. (In this, "toward" would not sound right) So, it really depends on the sentence. Please let me know if you have any additional questions. Hope this helps!