if say diffence two word by English. 「知らないです」= I have no idea 「知りません」= I do not know .These are very close meaning let’s divided one is 「知る(know)+~ない(word of negative)+~です(word of admit)」 other is 「知る(Know ) + +~ません(word of nagative)」 therfore one is adimit no knowlage others Just Negative sentence of 「知っています」 (I know). Grammer is both correct 。Usage is same.